Well.. This manga is super cringe. this review will be crude and straight to the point.
Plot
Seven empires. MC is guard of one empress. She creates some anti-war barrier thing sacrificing herself. MC and the empress use reincarnation magic. MC born after thousand yeras, get adopted by a countess (milf) and gets a bonus step sister. But the empress's soul is split into 6 parts and now resides in the princesses of the six empires. MC with his sister/mother and six princesses goes to magic academy and whatever...
The power system is also just random nonsensical garbage thrown together, which makes me think that if you don't know how to write fantasy, just don't ???.
MC is one of the main weaknesses. whenever i hear MC say that he's going to "save" someone, it was really cringe af. Felt weird because i read a LOT of isekai, harem, ecchi or other garbage, but this is the first one to actually make me physically cringe.
The fights are boring because it feels like everything is made up as the fight goes along. After the first 10 chapters, i usually skipped reading all the combat parts, and that's the only reason i had enough patience to continue reading upto this point.
The story takes itself too seriously. Like.. did you expect anyone older than 13 to read this with straight face? Even with 9+ potential waifus, i still can't self insert myself as MC, because he is THAT cringe. The story tries to be mysterious about the reincarnation, but i honestly couldn't care less. If you cannot be a good story OR a bad story (like self insert power fantasies), then you are just a boring story.
Anyway, i would usually recommend some manga just to pass time, even if they are not great. But this manga doesn't even qualify for that. Just skip this one and maybe try something else.