I remember this was an isekai manga but the main character is not reincarnated nor does he remember his past life. He was raised and taught magic and stuff like this by an old elf (the old elf says to him he is weak but in fact he is OP).
He leaves his home and goes on an adventure but soon he meets a noble lady being chased by some goblin chimeras. He saves her and she takes him to her home and after some dialog she says to him to become a magic teacher at her school and after a while he agrees.
The old elf was very powerful and the main character becomes even more powerful. He told him he was weak to not make him arrogant before he left to become an adventurer. I don't remember how he saves the lady (it was magic or a spirt/summon). She wants him to become a teacher because of his strength (to not waste his power/life?) and I classified it as isekai because it is like a isekai world (adventurers, goblins, guilds, magic, etc)
I remember he summoned something and in his chant it referred to Lucifer, but the spirit/demon was a small lady and did not had the name Lucifer.