What is the ruling on one who guides others on how to commit a sin, then repents from guiding people to it, but does not himself repent from committing it?

Watching anime is not forbidden in itself. Rather, what is forbidden are the objectionable elements it may contain.

Thus, there is no sin in watching it or in guiding a friend to it if it is free of objectionable content. However, if it contains objectionable elements, then one must refrain from it and advise the friend on the guidelines for watching.

Repentance for having guided someone to a sin is accepted, and repentance is valid for one sin without necessarily covering another.

If it is possible to advise that person, then it should be done.