Kaioshin
Why not give the MC an ARK survivor implant like in Avatar: A Survivor Lost on Pandora (written by The_Bip_Boop2003). You just need to give the MC the knowledge of engrams and a physical tracking tab, and as a bonus make all the things stored in the implant's storage space put the weight of everything stored distributed throughout the body, so you can do the MC put stones inside, to make him train his body evenly and literally all the time, and by adding a little gravity magic we can increase the effects of the training even more.