Astral Seed + Fusion

[icefractal]

I think it works, but doesn't mean the the resulting creature is your PC.

Whether Astral Seed makes Fusion permanent is up for debate. Personally, I think that while it shouldn't make effects in general permanent, this particular one may work because it actually creates a new being. So the fact that said being is gone by the time the seed grows doesn't seem to prevent it any more the the usual "being dead" would.

However, if it is a new being, then the fact that its mind is partially derived from you doesn't mean you now control it as your PC. Like for example, if you permanently mind controlled the Tarrasque, or used diplomancy to make someone a fanatic follower, they're still an NPC; you don't start playing as them.