I always thought Kaku following Lucci in Cipher Pol 0 was inappropriate since dude was the only one showing genuine regret at the end of Enies Lobby.
Now he's stuck once again in a position of inner dilemma, cause he knows that:
- if Lucci enters the control room, Stussy is done
- if Stussy gets killed, he will be emotionally hurt by it
- if he tries to stop Lucci (which he can't) he'd be considered (by Lucci and himself) a traitor
Kaku is stuck in a lose-lose situation. He's an intetesting character, writing-wise, the only problem I have with him is that he has no reason to still be an assassin in the first place.
He simply don't fit, and kinda vanifies his words in Enies Lobby...
Yeah, that's why he's asking her to go off.
He knows Lucci will kill her if he finds out she's still alive.
Lucci won't attack him though, there is too much respect between them and Kaku is pretty much the only character Lucci has uncharacteristically shown concern for.
Though the cover story implied there is bond between all members of CP9
Him and Lucci joining CP0 after the cover story was weird though.
It may make sense, if they made a deal to get revenge on Spandam. Spandam now calls Lucci his boss, and Lucci/Kaku are his direct superiors. Maybe the reward to rejoin, was to inflict this kind of humiliation over Spandam.
As for why Kaku is still an assassin, I guess he doesn't know anything else (aside from being a shipwright), plus his friends all joined there. Too ingrained into him at this point I guess.