It's not Japanese I don't think, but the tag fits!

Hanging naked in a closet surrounded by bondage gear?

ejaculating! *zing*

These are aptiasia or glass anemone, they are very rarely kept on their own in single species tanks, and can grow pretty large.

They kill everything that they touch (tens to hundreds of dollars of better coral) and will eat fish when they get bigger.

They also break off pieces of themselves and grow new clones all over the aquarium.

The most effective method of killing them is with a natural preditor like a nudibranch, butterfly fish or shrimp, pastes like this don't work too well.

If you get individual small ones on new live rock then a turkey baster full of boiling water works very well. you then suck up the remains by releasing the bulb.

I realise that this comment makes me sound like a serial killer.

I does give a new meaning to your name.

I fixed-ed-ed it.

This is less of an animal than a fly or spider you might kill on a regular basis.

It's a jelly fish in terms of nervous system complexity.

Luckily there's plenty of natural predators for these things. The problem is that in captivity those predators either die as they don't eat anything else, or they eat anything but aiptasia.

These things sting clownfish. They can't host them.