Tensei Shitara Kozakana datta kedo Ryuu ni Nareru Rashii node Ganbarimasu (Associated Names)

When I woke up, I was in the shape of a fish in the river. Why do you look like a fish, and who are you in the first place? While leaving only the memory of being human in the previous life and being puzzled by the loss of all memories of himself, the days…