Mugen no Juunin: Immortal S01E16 - Act Sixteen - Altered Limb

Ever since the Dewanosuke incident, Burando kept making blunders. He is finally thrown in solitary confinement by Habaki, and goes insane. But as a result of his madness, Burando grasps something important about the immortality experiments. That humans are essentially otters. Meanwhile, Rin and Doua resolve to infiltrate Edo Castle to rescue the surrounded Manji and Isaku.