It's a very short piece from a small scanlator group and I think I discovered it through this website.

The story starts off with this man in a military uniform (probably Japanese) walking along across the snow to this other gentleman in a cape.

They look like men's men board shoulders and wide backs. Not monstrous bodybuilders, but something akin to Michelangelo's "David"

There was a little dialogue: something about a fail Coup d'état and the soldier being executed tomorrow. The long haired man (enough to cover his nape) doesn't really care.

At a second floor of some abandoned establishment, they have sex.

The last article of clothing off from the soldier was a fundoshi, it revealed some good ass.

While in sex, the long haired guy bit him. Turns out he was a vampire.
He told the soldier to choose the way to die, should he drain his blood? Or should he turn him into a vampire and wait for the sun?

He chose the latter.

It was a long afterglow.

Anyways, that's how it went.
Additional details: the atmosphere was sketchy and (literally) dark; and there were around 10-30 (EDIT: IT'S 20; typo) pages; it's freakishly short.

Many Thanks for your help.

Hey! It sounds interesting. I don't think it's this story, but Akai Hana is what I first thought of when I saw the name of your post. You might like it to cuz it's a similar concept. Good luck finding your manga!

Moved to Yaoi/Yuri~

It's probably Murder of the Raven of the Universe.

Quote from Yenoh

It's probably Murder of the Raven of the Universe.

I second this!!! o.o

Quote from Yenoh

It's probably Murder of the Raven of the Universe.

I'm very thankful. TT-TT

(Yes, this is what I was looking for.)