Odin and Narugami
This is from Volume 4 of Matantei Loki Ragnarok. It's pretty much Odin's first appearance; I think he may have appeared in the previous volume, but he didn't do or say anything significant, so it doesn't really count. I like this scene because Odin and Narugami continually go from cool and serious to silly and back again, and also because we finally get to see some father-son interaction between them (spoiler: okay, so this isn't really Odin, but it was still nice to see them together).
Volume 04
Volume 04