Uh, I think that's Len not Rin.

Tha artist says its Rin. Also Len got different hair.

I think that really is Len since "he" says at the beginning: datte rin, pantsu...

Also, post #181492 has Len wearing Rin's hairclips

Mystery solved once this gets translated. Do note that in Japan, children (and sometimes, some "adults") refer to themselves in 3rd person.

This is Rin. She refers to herself in text.