It's not using each other! He used her, that's all there is to it.

[All his mother wanted was a father for her kid, to have back in her live the man she loved. She didn't "use" Mitsumasa, she was the one used and discarded.

He still refuses to come down, crouching a bit on the branch as he answers the question.]

I don't know. I have never seen it, but it's not sex, it's completely different. And it doesn't hurt anyone.