Risto

One of the coolest nicknames for Christopher! It completely excludes the C; not common in other diminutives. I think it could work as a standalone name as well. It doesn't sound childish to me, which is also uncommon for a diminutive. It sounds tough as guts. Rrreeesto!

I think that this is a great name! It's a nice, unusual alternative to other short forms of Christopher while still being familiar. I would recommend this name!

I know a cafe with this name.
Risto, rather nice name actually.