Definitely Nic(k). I think it is such a sexy, strong and masculine name/nickname. It's my all time favorite nickname.
Nico is nice too but I'm not a fan of
Cody and I can help but think that
Cody kind of ruins
Nicodemus which I think is a great name.
I can't come up with any other nickname than Demy/Demmy (don't like it)