I'm trying to find a manga where mc is researching magic in a cave. He has a familiar (some kind of fox/wolf) and can't die because both of them drink something so he can research magic for longer... His familiar didn't want to drink it but the potion fell into his/her drink. After years have passed he finally goes outside and is OP with his ancient magic?
When he is casting the magic he is mumbling something in different languages. I know he came across a girl that when she meets him she starts to say the same thing when he is casting his spells. The mc has glasses. His familiar is red.