Battle for Legitimacy

Battle for Legitimacy is the twelfth and final episode of the first season the How NOT to Summon a Demon Lord series. It aired on September 20, 2018.

Synopsis
''The final battle against Krebskulm is won and the Demon Lord is restored to her former self. This, however, isn't the end of all of Diablo's trouble as Alicia has a favor to ask of him and his party.''

Plot
Outside of Faltra City, Edelgard and Eulerex along with a massive army of Fallen relish the fact that Krebskulm has finally fully resurrected. The two are soon joined by Alicia who is revealed to be the mastermind behind the entire plot to fully resurrect Krebskulm. As Galford cogitates over the situation at hand, Sylvie visits him and assures him that the problem north of the city will be dealt with and he should focus his energy on the threat to the west.

As Diablo faces off against Krebskulm and Shera uses the healing potions given to her by Diablo to treat Rem's injuries. For the time being, Diablo manages to dodge Krebskulm's attacks while laying down trap spells. When Krebskulm uses Darkness Breath, Diablo counters it with Volcanic Wall. On Shera's side, she uses the last of the healing potions on Rem hoping that she'll recover. Thankfully, Rem regains consciousness and informs Shera of Alicia's betrayal. Returning to Diablo's battle against Krebskulm, he struggles to fight against her as she now tosses stone coffins at Diablo who is in a pinch or giving away all of his healing potions to Shera. Right when a coffin was about to hit, Rem and Shera; Emile appears before them and takes the hit. Finally able to set thirteen spots to cast his grand magic, Diablo casts Apocalypse Abyss. Although effective against Krebskulm, it was not enough to destroy her. It was thanks to Rem being shouldered by Shera that she manages to reason with Krebskulm which allows her to revert back to Klem. Surprised that Krebskulm changed into a young girl, Diablo asks if Emile would turn a blind eye to this, but he reassures Diablo that he's an ally to all women. Outside of the city, Edelgard and Alicia were about to face ridicule from Eulerex for another failed attempt at resurrecting the Demon Lord. However, Edelgard manages to distract the Fallen army behind him allowing Alicia to escape.

Eventually, Sylvie meets up with Diablo and group thanks them for their efforts in stopping Krebskulm, but deduces that Klem is Krebskulm. Despite the protests from Rem and Shera, Sylvie details that Klem may have summoned the army of Fallen outside of the city, therefore precautions must be taken. Hence Diablo suggests that Klem become his slave and she agrees to it. Thereafter Diablo follows the enslavement ritual and Klem becomes Diablo's slave. Afterward, Sylvie reports the results to the recent events to Galford, who was already aware of most of it due to his information network.

That night in Diablo's room at the Peace of Mind Inn, the group get ready to retire for the night until Alicia appears and takes Shera hostage with a knife. Klem threatens Alicia to release of or else she'll kill her. Alicia promises to allow Klem to do whatever she wants to her so long as Klem helps her with something. That something was to heal the heavily wounded Edelgard and because she's a Fallen, only Klem would be able to do it. Alicia also details where and how Edelgard received her injuries and confirms to Diablo that she was in cahoots with Edelgard all along. Following Diablo's request, Klem heals Edelgard who prostates herself to Klem for her merciful act. After Klem briefs Edelgard on why and how she's back to her old self, she orders Edelgard to stop killing mortals as a show of loyalty towards her. To that order, Edelgard agrees to obey Klem's command. Once that's all settled with Alicia resolves to face whatever consequence Diablo and her group will do to her. Instead, Rem first asks Alicia what made her side with the Fallen and in response to that, Alicia blames her upbringing being surrounded by shallow Nobles and Imperials. Listening to Alicia's story, Diablo relates to it from his own experiences when he was back in his own world. Again, Alicia asks Klem if she doesn't despise the mortal races, to which, she annoyingly agrees that she doesn't. Hence, Alicia tries to stab herself in the neck, but her knife is dissolved by Diablo's magic. He then gives an eloquent speech about how Alicia should find a new purpose to live for, which brings her to tears. Becoming flaccid over his lack of MP, all of the women now also including Alicia and Edelgard volunteer to help Diablo recover his lost MP, much to his dismay.

The following day, Diablo, Rem, and Shera see Alicia off and later the girls get into an argument over what food they'll eat for dinner. They soon choose to settle the argument by having Diablo kissing the one whose side he's on. However, he refuses to choose either choice as he's Demon Lord Diablo.

Characters in Order of Appearance

 * Eulerex
 * Edelgard
 * Alicia Crystella
 * Celestine Baudelaire
 * Chester Ray Galford
 * Sylvie
 * Diablo
 * Krebskulm
 * Shera L. Greenwood
 * Rem Galleu
 * Emile Bichelberger
 * Mei

Differences from the Light Novel

 * There was more to Alicia’s escape to the city with Edelgard than what was shown.
 * The ending differs significantly.
 * Alicia focuses her hatred to those in power rather than the mortal races as a whole.
 * She becomes Diablo’s spy in hopes to eventually undermine the kingdom.
 * As such, the battle with Kuzukage is also omitted.
 * The anime instead has a "harem ending" that did not occur in the light novel.