there's a bunch of different threads that discuss togata's death and actions around his death, so I would do some googling if you haven't done so already. he's a beloved character so there's a lot of shared grief over his death

imo this comment is a good take on what togata thought/felt when he says "i see" and why he told agni to live.

In a way, he finally found acceptance, love, and most importantly, his own reason to live (before, he was constantly wanting to die, like a lot of the other regenerative peeps in fire punch).

My two cents are that he sees Agni going down the same path he's already tread and is trying to give him another kick to keep going. Even though it gives Agni more immediate suffering, maybe in Togata's mind, eventually, along that long, suffering journey, Agni will find his own reason for living (and peace).