Just before the mission starts, Omi complains about the snow and cold weather (the mission takes place on Christmas).
Ken: Omi, it's okay if you get closer, just don't bother me.
Omi (a bit annoyed): Ken-kun, I am here to help you! We don't know what may happen during the mission.
Later, during the mission, Ken tells Omi to help him with the target (Ken and Omi share their first kill).
Omi (excited): Ok! I will use the bow-gun!
Ken (rushed/annoyed): Use the darts! [or Darts will be enough!]
Omi (mumbles disappointed): ... I wanted to use it just in case.
After the mission Ken and Omi are walking together, Ken is munching on something.
Omi (curious): Oh, what are you eating?
Ken: Sweets. What? Can't a guy have something to eat? [Ken says it like Omi was bothering him a lot, but he isn't angry]
Omi (laughs): This isn't what I mean. It's just not like Ken-kun [to eat sweets?]
[As for the sweets Ken is eating, he visited a church before the mission and got them from a little girl as a Christmas present.]
I love the second mentioned scene because
btw, Have you noticed that Omi complains about being cold quite often? :) He does the same in the Holy Children CD drama and Forever White (the novel). The people with him (Youji in Holy Children; Ken in Forever White and First Mission) don't seem to mind.