UPDATE!!
Characters:
Racine: 184 cm (6 ft) brown/black hair - is the uke to Kain.
Kain: 190 cm (6 ft 2 in) blond guy - is the seme to Racine, Father of Gian and Uke to Verne, the "boss"
Verne: 189 cm (6 ft 2 in) shaggy black hair - is the seme to Kain and is in love with him; possible seme to Gian.
Gian: 180 cm (5 ft 9 in) blond guy - son of Kain and possible Uke to Verne; Racines rival.
Tom: Assassin; in a relationship with Jerry.
Jerry: has a scar on his face; assassin; in a relationship w/ Tom; traumatized from experimentation.
Red cross: Tall blond women, same company assassin as Gian and always helps him.
The story starts out with Racine as a child and Kain as a younger assassin. He kills Racine's mother while she was doing laundry and while Racine plays with other children. When Kain leaves he takes a picture of his work and walks away to bump into Racine and this is the first time they cross paths.
Going into the future when Racine is in his teens, Racine is a pick pocket.
Kain and Racine start to live together maybe because Kain pitied him or maybe Kain recognized him. They have a sexual relationship with each other.
Racine becomes an assassin maybe following the footsteps of Kain. Kain disappears often leaving Racine along so Racine has sex with other men to lure Kain out.
Racine goes to visit his mother's grave to and sees Rozion also visiting her grave and crying.
He gives Racine an address regarding details of his mother. He goes to the address and you see a black long hair guy with the tattoo on his back just like Racine.
It appears this guy was sent to assassin Racine's mother a long time ago, but he did not do it.
Racine gets Kain a present for xmas and while trying to find a place to put it so Kain can see it, Racine comes across a photo album of pictures of murdered people that Kain likes to take after his killings.
In this album he finds a picture of his dead mother and cries. On a side note everytime he comes across Gian they fight and this is all the relationship they have so far, nothing sexual.
o.O
Kain was a young assasin who didn't work with anyone. One day he goes on one of his assassin missions and does his job. While he is leaving he sees another younger black hair guy kill another man.
This guy was Verne also in his young youthful days sees Kain and wants to get rid of him because he is a witness to the killing. Kain and Verne does not know each other are assassins.
This is where Verne falls in love with Kain. Their cross paths a few more times and then it turns out they begin a sexual relationship for a long time and is still on-going even as Kain is with Racine.
Those times when Kain disappears from Racine he either working or with Verne.
It appears although Kain is the seme with Racine, Kain is actually the uke with Verne. Verne really loves Kain, but it seems Kain does not love Verne in that way.
When Gian was a child and holding the hand of his mother, the mother runs up to Kain and tells him Gian is his child. Kain pushes her away and leaves.
Due to this Gian's mother tries to kill Gian. Going forward you see Gian with long blond hair in a hospital being examined.
He thinks back to the time how his mother tries to shoot him and he is inraged and picks up a scaple and kills everyone and runs.
Gian runs into a few men and kills one of them. They were about to shoot him but those men who work for Verne was stopped by Verne. Verne decides to keep Gian as he seems to be a killing machine.
While living with Verne and after Verne and Kain has sex, Gian always crawls into the bed and cuddles with Verne.
As Gian is now older, you do not see him interacting with Verne anymore so its unclear who he works for.
Yup, that's pretty much all I found out; Fascinating isn't it.