Any short manga recommendations?

I just finished reading Deadman Wonderland, which was 13 volumes. I thoroughly enjoyed it. Anyone else know of good manga that's on the shorter side? I'd say I'd prefer it to be darker as far as subject matter goes, but anything action oriented is up my alley.

Danshi Koukousei no Nichijou (Daily Lives of High School Boys)

This manga is easy to finish. This is by far the first manga I ever finished.

Petshop of Horrors

Fuan No Tane?

If you haven't read Death Note there's only 12 volumes to that