Under the Skin MangaN/A
This contains two short stories, one about Bun and a new kid he's found to replace Satoru from Heat; the second is a look at Bun and Daisuke
Miyamoto Kano's "Walker" universe timeline:
1) Are You Enemy?
2) Not/Love *licensed
-- Not/Love dj - The reason why we live together
-- Not/Love dj - Dog Days
-- Not/Love dj - Demonic Conversations
-- Not/Love dj - Brand New Lover
3) Heat (Miyamoto Kano)
-- Under the Skin
-- Lizards, Angels, and Daemons
The ones in ( -- ) are doujinshis.. They give background or "add into" to some key points in the main story line. So you're not really missing anything even if you don't read it.