Dabit deus his quoque finem

Dabit deus his quoque finem is the 4th volume in the Youjo Senki Light Novel series.

Short Summary
The day of the Empire faced another crisis.

Russy Federation start to mobilize their troops.

Who will win the Eastern battle? Who will succeed?

Will Tanya finally find her own peace and win against Being X?

Chapter I: Long range reconnaissance mission
After a few months in the sand, Tanya and her unit are all recalled from Southern Continent back to the capital. Tanya immediately assumes that they are getting vacation and they all move leisurely.

On the landing platform, she sees that Major Ugar is waiting for them. She believes that he is here to welcome them and give them some nice luxuries so she acts in a happy manner and that everything is fine. He subsequently hands Tanya confidential orders with a time seal and loads the 203rd into a spy plane in the middle of the night and sends them on their way, saying that they are part of an exercise.

On the plane, Tanya opens the orders and is told that several spies in the Russy Federation have raised the alarm against potential invasions and immediately went dark. This in turn caused Operations to call them back for a secret recon behind enemy lines. They land just behind the border and because they are there in secret, they have to rely on doing their job without magic (i.e. Tanya is in trouble). Despite her small stature and physical strain, she decides to scout further with the rest of the company commanders; (re-shuffled losses on various battlefields) Weiss, Visha and Grantz.

They eventual spot a large assembly of units including several divisions of infantry, tanks and a squad of railway guns. While Tanya orders Visha to setup the radio (one of her new responsibilities), the railway guns open fire, signalling the start of the war. While they discuss what to do now, Tanya spots a large and unprotected stash of railway shells and gets happy thoughts about shooting liberty, freedom and the free market's greatest enemy, the commies. She sends over a message to Operations and she is given the go ahead. After their first strafing run, she is surprised that there are no mages coming to intercept and continues her attack.

The scene then cuts to the remembrance/victory parade of the war in the federation in 1980, a reporter interviews a war historian. The historian explains that the reason for the sudden attack was the paranoia of the upper echelons of the federation at the time, that they all suddenly believed that the empire was going after them, so they decided to strike first. Their own history/propaganda states that the kind and benevolent Josef was having terrible dreams after taking much care about his peoples needs and he confided into his best friend, which to his surprise was having the same dreams. So they decide that they must act on the evil to the west.

Meanwhile from the prospective of the Imperials, the country was in a state of chaos that the Federation would join the war now of all times and some had trouble believing it. But when they remembered that the same thing was done to them by the republicans and what happened to those who overlooked them. They all spring into action. In Southern Continent, Romel starts to realize how valuable a subordinate like Tanya can be, being forced to manually control all the mages on the lines once again. However, he makes his condolences to the federation and that not even he would want Tanya as an enemy.

Chapter II: Goodwill visit
Back at the homefront, things are in chaos as the federation is pushing harder on the eastern front than expected and they push into the Empire further than expected. But all of the upper echelons drop everything at a moments notice when they receive a message that Tanya has an idea, she asks permission to raid the federation capital Moskva. The plan sounds so crazy that even Zettour, their de facto commander, is doubting its possibility. The sole person to speak for Tanya is Colonel Lergen, the man responsible for handling all the medals and commendations of the 203rd. He says that Tanya has already done this thrice before (Dacia, revolving door, Romel).

Zettour then says that even for her this mission would be almost impossible but Lergen replies that she is asking for permission. Meaning that whether or not it can be done is already established and that she is merely asking whether or not she'd catch hell if she did it. Zettour then starts to get convinced but asks whether it is actually a good idea to let Tanya of her leash. Lergen then simply points out that ignoring Tanya's hunting sense had cost them dearly with De lugo. Eventually Zettour caves and Tanya is given permission.

Tanya and co. reach Moskva. She remembers that the communists are quite heavy on the oppression of the free press and such she decides to make a mess so large that no one can deny it. She spits up her team and she goes for the people's palace while Weiss goes to remodel the bronze statues around the city, Visha is going after the secret police and Grantz is assaulting the red square. Tanya is unusually happy with their current status as she is going after actual communists, which she deems the enemy of all her popular beliefs (freedom, liberty and free market) and that she deems that all who follow her beliefs must fight against communists. A few minutes, a terrible counter attack and one imperial anthem on the loudspeakers later, all but Grantz accomplish their missions, as the Red Square is surprisingly heavily fortified. Although she wants to go after Josef (Stalin), she can't be 100 percent sure that he is in the red square so its given a pass.

Afterwards she decides to make a propaganda video on the red square, having Visha raid the local film studio's for some equipment and flags and a camera. She then makes a video of imperial soldiers marching through Federation streets, waving the imperial flag and burning all the federation flags they can find. Unfortunately for Tanya the number 2 man in the Federation, Loria, spots her and falls in love with her. Loria vows to do everything in his power to capture her, break her, and ravish her. So he decides that the Federation needs to release the prisoners from the lageri, particularly the mages (who were loyal to the previous Imperial regime), and win this war.

The news that the Empire had successfully raided Moskva is shocks the entire world, especially the empire. While the citizens are elated, the upper echelons were furious. They only thought that Tanya was going to make a flyby to draw away troops from the front, not burn down half the government and eliminate any possibility of peace. Meanwhile in Londinium. Churchill is just as shocked as the rest of the world to hear that a regiment of over 100 mages was able to breach into Moskva. He initially thought that just a few mages only managed to get into Moskva airspace, but the Commonwealth embassy reported that the damage was so large it couldn't have been anything else. The entire military council sinks at the thought and immediately does something about the lack of security in their own capital. Churchill asks about a counter attack in Berun but the council replies that the Empire still has its magic warning line on its west border due to the fight against the Republic, so a sneak attack is impossible. But the entire ordeal proved shocking enough for the Allies that they decide to pull back all the forces that were supposed to aid De Lugo.

Chapter III: Magnificent victory
After the general staff agrees that Tanya went overboard, they sent Tanya to the rear of the eastern lines to be on standby and provide cover for the eastern army. While on standby, she gets a report that the nearby town of Tiegenhoff is surrounded by several divisions of enemies and that the 2 divisions stationed there are requesting for aid. While thinking of whether or not she should interfere, she receives new orders from Strategic HQ. She immediately decides to aid Tiegenhoff as it's likely to be a lot easier then whatever the hell Strategic HQ has planned. But after double checking the orders and the map of Tiegenhoff, she finds that the 2 orders are not mutually exclusive and that Tiegenhoff would make an excellent point for a counterattack.

Tanya requests for intelligence and is delighted that there is no enemy heavy artillery in the Rhine and as such they can just rush over there without issue. Visha, off all people, is the one to object to the plan. She reminds Tanya about the railway guns that were stationed at the border prior to the attack. So even if the Empire has been pulling back the lines, they should still be in range of those guns. But Tanya rejects her claims, stating that railways guns at that range would require observation scouts, and if they were there, they could just kill them. Visha caves and Tanya laments that they don't have any presents to give to the 2nd and 32nd. Weiss however, interrupts, stating that Visha has won several rounds of booze and cigarettes in card games against the Romel HQ and subsequently dumped them into the battalion treasury.

The 203rd arrives at Tiegenhoff and sees the town surrounded by 4 divisions. They attack 1 division and punch a hole through their lines and then go to attack the enemy commanders in another. This in turn causes the 32nd to breakthrough the gap left behind and eventually routes the enemies.

The next day, the federation military command laments their own position, they had reports that the imperial lines are falling back in the center but the flanks are holding strong. Causing them to believe that the Empire is trying to something similar to what they did to the Republic. They try to request to change actions, but the upper echelons of the communist party reject the idea outright because of what Tanya did to Moskva and that they must push forward at all costs. This however is easier said than done as the attack on Moskva caused nearly all the mages to be pulled back to Moskva, giving the Imperial mages (mainly Tanya), free reign over the skies and allowing her to destroy all the supply depots in the rear. But the Federation military does receive one piece of good news, they received intelligence that the mage unit responsible for the attack on Moskva is in Tiegenhoff and the federation military is going to use it as an excuse to break the encirclement.

The next morning, Visha smacks (she literally smacks her) Tanya out of bed, reporting that 8 divisions are currently on their way here. Tanya gets her crew into the air to try and delay the enemy while the other 2 divisions begin the retreat, realizing that the communists must have seen through their plan somehow. She finds the first division and begins an air raid, causing some damage and assassinating the majority of their officers. But to her surprise, there are no mage or air units. The soldiers request another strike against the division but Tanya has none of it, despite her being the only one against the attack. She states that the enemy mages are likely in wait, since there have been many reports of fierce battles for air superiority against them so she diverts the soldiers elsewhere. After the finding and harrasing the 8th division, all her units are dead tired and they still haven't found any mages. But then it hits her, the units on the eastern front are only a small part of the army while they are facing the entirety of the federation army, so if they actually have a chance of maintaining air superiority now, then the entire air force of the Federation must be useless. As such, she laments her own abilities and avoiding the possibility of destroying 8 divisions single-handedly.

Chapter IV: Reorganization
Afterwards, Tanya is recalled to the capital, where is put under questioning/on trial for what happened in Moskva as it blew apart any chance of peace with Rudersdorf as the judge and Zettour as defense attorney. Tanya is formally charged with disobeying orders and attacking the civilian population, but she pleads not guilty. Zettour defends Tanya, saying that her actions were necessary for the military and that she did take precaution against civilians, attacking only government targets and every single one of the military officers present support Tanya. Tanya is eventually found not guilty and Zettour starts to ask where she wishes to be posted next.

Tanya responds by requesting a spot in the rear, shocking everyone. Zettour asks why and Tanya states that if people aren't happy with how she does things on the front lines, she doesn't want to be there. Zettour almost looses it completely with Tanya acting childishly, he calms himself down after reminding himself that Tanya is an actual child. He asks what it is she wants and Tanya replies that she wants to be placed in combat research and strategy, wanting to determine what is the best way to use military forces rather than just being one. Zettour gives Tanya 2 months on the Dodobird Strait to determine new combat tactics and strategy and her results will determine her new postings.

Meanwhile the Commonwealth ambassador to the US tries to buy arms but he is required to settle for scraps.

Back in the Federation, the highest ranking members of the Party have a meeting about what must be done. Loria asks for the mages in the concentration camps (gulags) to be released and that they and the empire can just kill each other off. Several other members object, stating that the mages can't be trusted. But Loria counters by saying that those who are against the idea must believe that there are enough forces in the Federation, thereby implying that the ones who objected were the ones at fault for the attack on Moskva. So none eventually object.

Meanwhile, Mary Sue is training in the Commonwealth with the rest of her friend from the US/Entente alliance. All the recruits there continue to overhear that the Imperials are conducting air superiority battles over the kingdom and that the Devil of the Rhine has single-handedly killed a company of mages. Mary states that the devil has to be from another planet in order to do that, since she herself has trouble with shooting alone. Some of the boys want to go pick a fight with the devil but Mary says that is better to think of a plan to survive the devil first.

Chapter V: Battle of Dodobird
After almost getting shot in the ass by a friendly squadron of planes, Tanya is required to attend an officers meeting. There they were informed that intelligence had confirmed that a volunteer unit from the US had arrived and is currently training on Commonwealth soil. There they try to decide on how to deal with them should they try to fight. Tanya states that international war time law doesn't actually take the nationality of the soldier into account, if they follow Commonwealth orders, they are Commonwealth soldiers. But the rest of the officers think that it isn't a good idea to provoke the US like that so they decide to leave this matter up to the rear echelons.

Tanya gets back to her room and thinks that their treatment of the volunteer soldiers won't affect whether or not the US is going to get involved. So Tanya decide to launch a preemptive strike on the soldiers to warn the US (and its democratically voting citizens) that full mobilization may not be a good idea. She and her unit take off but find that the weather is terrible, so they bunch up and stay out of sight.

But at the US base, the soldiers including Marie are rushed out of bed and informed that 2 minutes ago, the Devil of the Rhine has been spotted nearby and that they are going to have to be the ones to intercept, since she is so close. Marie asks who they are dealing with and Lt. Colonel Drake (the guy that was spying on Tanya back in the Entente alliance and subsequently got his observation base blown up by her), who is appointed as their liaison. He states that the Devil is an entirely different matter, even compared to other named mages. And what's worse, her skills in commanding a unit are on par with her combat skill, making her a nigh unstoppable force in the sky.

Meanwhile, western imperial command issues a no fly command and all the unit are ordered to return to base, except for the 203rd. They receive orders to rescue the commander of the 114th air division, who managed to get shot down over enemy territory. Tanya replies that they don't have the authority to order her around, but imperial command replies that they already have received permission from strategic HQ, so they do. Tanya then fans out her squad until she intercepts chatter that the local police have already apprehended the target. She deploys Visha and her company to take back the target and calls in a favor from the friendly air unit to airlift the target back to the Empire, deploying 2 other companies to find a suitable runway. But after the orders are issued, she spots 2 US battalions over the horizon.

The commander of the US forces orders 2 companies to attack the last imperial company at 8,000 feet but drake stops him, knowing exactly who is waiting up there for them. The commander is insistent in going after them, but drake requests that in the even that the commander is shot down, he gets command of the unit. Although the commander makes note that requesting inheritable command of a unit of foreign nationality isn't a good thing, he gives permission. The 2 battalions line up in firing squad but at the moment, Tanya and her unit bolt down from the skies, easily dodging their shots and making a strike, killing an entire company including the commander.

Drake immediately orders the retreat, but Tanya and her company do not let up on the attack. Mary tries to rush Tanya to protect her comrades but Tanya seems to be out of ammo at that very moment. So she pulls out the magazine, throws it at Mary and then butts her in the gut while she blocks the empty mag. Mary recognizes the gun that Tanya is holding so she tries to grab it, but Tanya quickly backs off, reloads and unloads on Mary, but she survives.

Chapter VI: Operation Door knocker
Tanya is recalled to the capital to write up reports. One report suggests that an adhoc combined army kampfgruppe, a temporary and smaller version of a brigade, be formed.

While Tanya is now convinced that she can now stay in the rear and write up more reports, Zettour decides to give Tanya a combat group. So now Lt. Col Tanya must form a kampfgruppe in 5 days. She will be deployed in 10 days then fighting within 21 days.

Meanwhile, at Moskva, Federation leaders are discussing what needs to be done after their invasion army's defeat. Loria suggests that the Union withdraw and draw in the Reich's forces to fight a long drawn out war. The Federation should fight more battles in their cities, where the mobility of the Reich's army is limited, and try to bleed the Reich dry with guerrilla tactics. The Federation can withstand the losses but the Reich cannot. Also Loria begs Josef that he wants Tanya as his prize. Josef agrees to both.

That ends 470+ pages of vol 4.

Thanks to u/MSG_Johnny2 who posted the summaries at r/YoujoSenki.