Write what you want with the characters you want. If people are affected, let them be affected. But there people that will still read so write for them and for you :)

Ofc. We're writing fiction anyway. Most characters only share appearance with the idol anyway as none of us know them. Keep going. Write whatever you want to write.

And if people don't like it, they can simply ignore it.

Why not? I mean, yes, they are a couple, but that doesn't count in the fanfiction world in my opinion. You can write about whoever you want. It's just work of fiction, it won't affect the reality. Just let loose your imagination.