Vague spoiler?
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One of them is a clone but they are not his father, they are related but they are not father and son. We already know 15's father is another prisoner (the only escaped prisoner from nanba). Also, Shiki (led by white haired guy) does a lot of experiments bc they were the ones who experimented on Musashi (Mr flames) in the past and are related to the whole Elf thing. Quite a bit of information is revealed near the end!
Spoiler…
According to the Nanbaka wiki, number 610 is Jugo’s father and the white haired guy is his grandfather from his mother’s side. The grandfather created a younger clone of himself which rebelled against him and becomes the founder of Nanba and Haaku. I don’t know how accurate this info is, but it seems to make sense story wise.
Hmmmmmmmm????????¿ (゜o゜;
Spoiler
I did not expected that, number 15 father is the founder of nanbaka, then I presume that the white one is his twin or clone, then this twin or clone experimented with number 15?????
Then who created clone of number 15??? His father?????
I'm confused