I amend my comment about Xen not being omnipotent...

'Remember, there are too many people, too much belief." - I don't quite understand the context of this phrase.

Suddenly, Xen appeared next to Ian - can you find a way to describe it other than "suddenly"?

Very good. I can't wait until the next chapter. Your two main characters are coming together nicely.

grim covered hands - Grime not grim

cement and fall flat on his bottom - Given the rough nature of the setting, the narrative should probably follow to some extent. 'Flat on his ass' would probably work better, especially for a T-rated fiction.

a safe wherein he kept his stash of goods - wherein? really? Although it's correct... it's distracting. I don't recommend using it unless it's for a specific character's dialogue, or something else that's really stylized.

I definitely like Ian. He's a likable foil to Xen. However, his rebellious existence lessens Xen's evil omnipotence and makes Xen seem a little bit more like a caricature to some extent.

"From his time spent in the sun, his hair had taken on a bronze and yellow hue, streaking out from his black hair" - Which man are you describing here?

"...so focused that a fly would be terrified to be caught under such a gaze." - Poetic, but kind of distracting.

back-up/backup - I'm not sure which is correct, but if both are correct, then choose one and stick with it.

"...wide open seas where human smells did not exist." - that's not entirely true. On the tallships there was always a smell. Sometimes it was from the bilgewater, sometimes it was from body odor of the men (who wouldn't have any sort of fresh water to bathe in), and sometimes it's from the tar on the ship itself. Things might be better for the captain or out on the deck though...

Depending on what time this story is set, be careful of the geography and remember that NYC has a lot of reclaimed land.

I think ship names are generally italicized.

"ruby red blood" - again, you can probably do better, something more grisly.

Interesting setup. The setting is interesting, the dialogue is alright, and the characters are interesting so far. I'm interested to see how it goes.