Yukichi Fukuzawa vs. Ōgai Mori (Mansion)

The battle of Yukichi Fukuzawa vs. Ōgai Mori in a Western-style building is fought between Armed Detective Agency president Yukichi Fukuzawa and Port Mafia boss Ōgai Mori at the height of the Cannibalism operation.

Out of the two leaders' prerogative to settle the feud occurring between their respective organizations by themselves, Fukuzawa and Mori decided to end the virus mutually destroying them in a death match.

Prologue
Fourteen hours before the virus outbreak, the Agency and the Mafia continually suffer casualties and losses from fighting each other. Fukuzawa learns that Akiko Yosano, Kenji Miyazawa, and Jun'ichirō Tanizaki are cornered by the Mafia and soon fall back after Motojirō Kajii's Lemon Runway, Katai Tayama has been allegedly killed in his own apartment, and Mafia forces have dwindled in number.

Hence, Fukuzawa and Mori leave their respective hiding places to rendezvous in a mansion that only both of them know of. Two hours later, Mori soon arrives at the mansion with Fukuzawa awaiting him, recalling the "fateful land" and optimal location only they are aware of from their shared past 12 years ago. They have both decided to end the cannibal themselves through one of their deaths.

Battle
Mori activates Vita Sexualis and summons Elise, while Fukuzawa prepares for combat. Elise materializes a large syringe as her weapon and hammers it down towards Fukuzawa, who quickly evades it. She soon flings out various smaller syringes, all of which Fukuzawa quickly slices with his. Mori expects no less from the Silver Wolf, once the government's greatest swordsman assassin, and praises Fukuzawa's for not being able to even see his blade.

As Elise later strikes Fukuzawa with her giant syringe once more, Fukuzawa defends himself with his katana. He is later forced to muster his strength and cuts down Elise and Mori himself. The dismembered Elise begins to vanish and bids to await Mori on the other side before completely fading. Mori then apologizes to Elise, while Fukuzawa sheathes his katana.

With Mori's apparent defeat, Fukuzawa declares the end of the Tripartite Framework. Mori warns Fukuzawa that the latter's death may put an end to the strife; his death, however, shall only yield to a bloodier bloodbath and revenge-driven warfare by the Mafia. With Fukuzawa horrified at such notion, Mori quickly hurls a to Fukuzawa's neck, leading the latter to collapse.

Mori admits that he cannot win against Fukuzawa in physical combat, hence resorting to such verbal tricks to catch him off-guard. Fukuzawa wonders whether his loss has been destined, while Mori prepares to finish him off with his scalpel. However, in the midst of a calico cat, he gets interrupted by a tremor.

Aftermath
Fukuzawa and Mori find themselves in the rubble of the mansion after an implied explosion, with the cat transforming into Sōseki Natsume himself. The two are shocked to find their mentor who reprimands them for being quite bothersome disciples. Natsume informs them how Katai, alive after all, has sniffed out the Rats in the House of the Dead's hideout and beckons them to act instantly before their foes disappear again.

The two leaders deduce that Fyodor will most likely remain in his current location awaiting for news on their unknown fates, which is the perfect chance to strike back within twelve hours before the virus triggers. Natsume then places his trust on them for their counterattack.

Manga and Anime Differences
In the anime, Mori personally participates more rather than having Elise directly fight Fukuzawa as depicted in the manga. This includes how Mori also strikes Fukuzawa with his scalpels and later throws some more at Fukuzawa's direction, all of which the latter deflects with his katana. They soon get stuck in a blade lock, during which Elise emerges behind Mori to strike Fukuzawa with her giant syringe. Fukuzawa afterwards cuts her down together with Mori. Elise then dematerializes, while Fukuzawa sheathes his katana.

Furthermore, Mori explicitly takes notice of the cat before he attempts to finish Fukuzawa off. The explosion during Natsume's intervention is also shown in the anime, whereas the manga only gives a subtle implication of its occurrence.