I find it hard to believe that tensei is doing this shit for seimei because from what ive seen so far of him, it shows the complete opposite.
except for renren arc, all the things that tensei had schemed to haruaki had him involve in getting rid of his soul (which has seimei in it)
so it sounds like tensei just need the body for his goal and it does get confirmed later on
he doesnt care about seimei, he doesnt care about haruaki, just the body, a vessel.
and most importantly, when seimei did came back, we could see his reaction and his reaction showed that he DID NOT want to see him, like this is not a face of being pleased seeing someone coming back and he clearly wanted him to leave immediately. this man is afraid of seimei just like anyone else.
from his reaction, his goal suggest that he wants to get rid of seimei.
with that, this panel made it sounds like hes rather mocking seimei than being devoted by doing something to get seimei's favor
theres definitely a falling out that happened between them because we've seen in ch 135 and the "special thanks" illustration in vol 21 that suggest they had a close relationship (and which tensei probably had the upper hand in the relationship). but we dont actually know what happened to them after that so far and their relationship remain unexplored.
tensei's goal could still be for seimei just rather a twisted version of it but i just wanted to show evidence showing that his goal is anything but reviving seimei the same way the 3 gods were trying to do.