Grimmer is fucking great. And tenma is seeing unfortunately an alternative to Johan, proving a lot of the earlier claims true in Tenma's eyes. Unlike Johan, Grimmer was able to (eventually) move past Kinderheim 511 and not be a monster. But Johan hasn't, so (in Tenma's eyes) maybe he was always a monster and it wasn't just the horrific situation he was forced in. Again circling back to the central question, what is a monster and what causes monsters to exist?