Dreizehnn
I'm pretty sure that any caster from the age of gods can do exactly what Roman does, but with divine power as a medium instead of will power. I don't think Tamamo would be that impressed by him doing just that, on the other side if he could create a mini black hole or manipulate time then I think she would be impressed.
Thea siendo un Homunculo hecha para servir como sirvienta y guarda espaldas ella estaría diseñada para vivir una vida completa de humano debido a que su padre se la dio para que cuidara de su bienestar así que dudo que sea de corta duración como irisviel quien fue diseñada para ser el buque del grial razón por la que tiene poca esperanza de vida.
So eiznbern wish granting sorcery trait? I'm pretty sure it's not going to be as versatile as you portray it to be. Honestly I'm a little disappointe, Fate shines best when magic resembles real world occult stuff not generic dnd fireball/magic beam attacks. Also its supposed theme for powerful magic abilities to create a warped mindset, Shiki, Manaka etc. Would have been more interesting if Mc say was suffering a constant feeling of surrealism/dissonance from his isekai abilities.