Fusion Reincarnation FuRein

This story revolves around Rivera Ryu. A reincarnated person. Before reincarnation, his soul was divided into two parts residing in two different bodies. One being Mizutani Ryu a Highschool boy and One inside Demon lord Mictian .
Memories of only one part get transferred but personality is a mix of both.
The Goddess who reincarnated him didn't give him a Goal saying "If it is you, I believe you will find the purpose". Getting in a troublesome situation as soon as reincarnated.
The protagonist takes a vow "If it is a new world, I will set my own Goals".