FallenEnt
I can see where the block is coming from. Once you deal with this invasion, then have him become human and merge with humanity there is nowhere else to go in this world. Only viable ways are: 1. He goes past the portal and ends up in another world, not necessarily the one he expects. Monster Hunter, other Godzilla world (parallel where he didn't exists to begin with), or something weird like One Piece (I hope not), DC, Marvel. Point is, something unexpected. 2. He goes human in this world and finds out this is some weird mesh of fanfics, slice of life or weirder, like Stargate SG1, or other things. 3. Travel the stars and find other worlds that are either other stories or originals. 4. Short novel.