While I can enter and exit freely, Shoot and the rest can only use the portal to leave once they enter.

If that has gained life by assimilating with you, then I'd say for the time being that it's probably the Rainy Devil.

Which means that the aberration came one night without you noticing, latched itself onto your arm, and beat up your classmates, fulfilling your wish.

Please, stop! You're starting to erode along with me!

Whoa there... Natsu's soul has mostly fused with the Dragonoid!

An alchemist possessing the knowledge of human transmutation was assimilated by Pride.

They'll be incorporated into her.

So she merged with multiple copies of her consciousness at once?

While she was soaking in the water, she must have changed herself to water by accident.

Matoi Ryuuko, your body has been fused with Life Fibers, just like mine.

You're blending in with the snow! I can't tell where you are!

My talent is blending in with stuffed animals.