Are Darkins only weapons that are used to cut things? or are there more types?

I don't think that if there are riot will share this information with us before releasing such a champ.

"baaka the hammer of sqiush"

I'd assume they're all physical weapons like swords, hammers, and possibly a shield, but we probably won't know anything for a while. Darkin Armor would be pretty cool though.

Untill riot makes such champs. Then yes. For now its only varus's bow, Aatrox's sword and this next champ.