Are You Enemy?

This is the first commercially published work by Miyamoto Kano.

2) Angelic Conversations I
This is the earliest timeline appearance of Bun. He is 17 and he is a regular at Akio's coffee shop/tattoo parlor. Akio does Bun's forearm angel tattoo, while high which provides some amusement. We get to see Akio's philosophy on religion and his obsession with Angels.

4) Angelic Conversations II
Same time frame as Chapters 1 and 3. Bun tries to help Akio with his drug addiction, but it's a losing battle when Akio finds out about a new God eyez drug that lets one see Angels. Can Bun save Akio from himself?

Miyamoto Kano's "Walker" universe timeline:
1) Are You Enemy?
2) Not/Love
-- 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 on ( -- ) 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.