Despite them having separate Rewz Lab profiles with different biographical details (being from Chiba prefecture vs. Kami-Shakujii, Nerima), Kazunari Motoki and Kamishaku-jii are apparently the same person:
Twitter name being "神灼爺 / kazunari motoki",
this tweet saying "私は元木一成。", mastering on Re:LieF
being credited to Motoki on the album but
Kamishaku-jii on Rewz Lab's site and
Kamishaku-jii talking about mastering it, etc.
Motoki lived in Nerima at one point according to Facebook, so I guess that's where that whole thing came from.