ExtraordinaryMe
Interesting story. The only thing that In my opinion dosnt make any sens is his personality. Yeah sure he got an happy seconde life with monstrous skills, but his past was cruel. He sold himself for his family and endured tortue…. that has to have left some pretty dark marks in his personality. Keep going
To teach you magic Merlin he was a geand caster which can pretty much smack anyone down. he taught arthur (artoria) and morgan. He also has access to avalon, excalibur, caliburn, rhomnymiad lance and has access to fay and the lady of the lake. He also has demonic incubus heritage. You can devise a ritual where he basically adopts you and makes you kin, giving you a dragon magic core, magic resistance, incubus heritage, eternal life, To teach you martial arts,discipline etc you have li shuwen and yan qing some of the best martial artist. Achilles can give you better overall knowledge. For weapons like spear you can have scatach Lady if the shadows. For divinity i would say arjuna or karna Utilise all methods of power in dxd -magic -divinity -chi:ki -touki -weapons -nature energy, sage power