Sensui's Personalities Turn Certainty Into Compartmentalization
SPOILER!
As the fight continues, Sensui stops behaving like one consistent opponent because he is not one. Kazuya emerges with a gun-like energy weapon and sadistic enjoyment very different from Shinobu's controlled presence.
Itsuki explains that Sensui's mind divided after the trauma that destroyed his old worldview. Different impulses could exist without being reconciled because different personalities carried them.
Why it matters
Sensui's moral absolutism did not make him internally pure. It helped make him unable to hold contradiction inside one self, while Yusuke's entire personality is basically contradiction held together by loyalty.
Debut: Ep 085 - Spirit Detective Showdown
Sensui's End Is Not Simply 'He Wanted Humanity Destroyed'
SPOILER!
Myth: Sensui's only goal was to wipe out humanity.
By the end, Itsuki reveals that Sensui is already dying. Opening the tunnel is still tied to his judgment of humanity, but Sensui also wants to reach Demon World before his own death.
That makes his final motive more personal and less tidy than the ideology he used to recruit others. He wants to see the world he spent years defining from the outside. He wants to die there. He has built an apocalyptic plan around a moral crisis, but he is also a terminally ill man trying to choose the place of his own ending.
Why it matters
The revelation does not excuse Sensui. It stops the viewer from reducing him to the slogan he used to organize everyone else.
Debut: Ep 093 - Sensui's End