Thread:LucidPigeons/@comment-2175012-20160509175734/@comment-2175012-20160530015641

Essentially, Kai can be considered as a foil to Anjin in a few ways: both have hundreds of years in experience with alchemy (Kai still looks the way that he does, because of the Philosopher's Stone slowing his aging), both have someone who they express some care about (Satonaka and Nina resectively), among other things. The difference lies in their motivations for their research. After Nina (a 16 year old girl with the mentality of a 3 year old) died by jumping off a cliff due to assuming that she was a butterfly, her death greatly haunted Anjin's life to the point that he attempted to resurrect her. Kai, however, is primarily motivated by greed as evidenced by him nonchalantly passing clones off as merchandizing products. He didn't start caring for Satonaka at least until he started to attend the academy. However, while Anjin genuinely loves Nina/Musumi, and is unwilling to kill her (as it is against his principles to kill anything), Kai ultimately valued his research over the life of his friend, and kills him without shedding a single tear.

As for the scene in which he passes the pocket knife to Anjin, saying that he should kill Nina so that they could be even, this is him trying to make Anjin feel guilty about refusing to be his assistant earlier rather than any genuine sorrow.