I bought a manga in English years ago (which I have lost) and I've been trying to search for it online but as I can't remember the title I'm coming up with nothing.

It's a fantasy manga I think, and it possibly involves a boy being taken to another world?
I know he comes across a troubled boy wrapped in bandages who is originally hostile towards him but then gets very attached and follows him everywhere (and gets him to change his bandages a lot, maybe). I think the bandaged boy has an evil twin.

That's really all I can remember. I hope it's enough to trigger somebody else's memory...

I would say it's Beyond the Beyond.

Yessss! Thank you very much