Did he really die though? Couldn't he just have dissapeared after being wounded and watching Chinagi die? He would have then gone into a state of "hibernation" (he referenced sleeping himself) where his form restructured itself during the next 1000 years. The White Dragon could then easily have believed that the Black Dragon was dead. That's my theory at least ╮( ̄▽ ̄)╭
Also, literally says "reconstruct" in manga http://www.mangago.zone/read-manga/koisuru_ryuu_no_shima/uu/mpn_chapter-2291605/pg-2/
Wait so they killed black dragon before? But he’s still alive. I would just read everything again but I’m lazy. Can someone explain? Lol