
He’s a vampire hunter. I get a feeling a vampire killer is parents and the vampire hunters found him as a child. Either that or his parents were already hunters and were killed during a hunting job and one of the other hunters took him in so Tristan could take vengeance. That’s how 95% of vampire Hunter backstories go. The other 5% percent are he’s half vampire like you said and they wanted to use him because he really hated his father or mother for killing his family which is highly unlikely because as you can tell: those hunters are extremely “death to all vampires”

I don't think it's believable that Tristian is half-vampire because Ethan IS half-vampire. I'm not saying it's impossible, but it would just seem odd to me to have both of them be half-vampires. I'm leaning more towards Fujoshi Dotti's thoughts. I think Tristan's parent were hunters and/or were killed or Tristan was raised by the vampire hunters so that's why he is one.

Found this in an article on sexual instinct in both animals and humans:
Chemistry
The sexual instinct needs to feel the chemistry of being hooked into someone/something and have it returned. SX-doms can feel like a hunter waiting for their prey, or prey waiting for their hunter. They are sending out pheromones wherever they go, aiming to leave their “scent” on others. Their biggest fear is being undesirable or losing that chemistry. Not being captivating or interesting enough to attract a mate is devastating. To use the peacock example again, the male peacock can put a great deal of mental and physical energy into their display, and still the female might just not think it’s arousing enough to mate. The synergy that is craved in SX is a sense of simultaneous giving and taking (although the giving isn’t altruistic). It can be paralleled abstractly in vampire literature where the vampire bites and drains blood but the victim gains pleasure from it, or at the very least, this is usually eroticized. During intercourse or other kinds of mutual sexual activity, both people involved crave the other as an object to “take” but also enjoy “being taken” by the other. Both people are objectifying each other but getting what they crave in the process. This chemical synergy of objectification on both sides locks both people into a chemical flow.
Note: This kind of chemistry is not the same as love or connection, however, humans of course have the ability to mix love with sex. However the Sexual instinctual drive is a separate domain. Connection and bonding is more in the Social instinct domain. And love and intimacy are not instincts.
Possible examples of thoughts: Is there a building energy between us? Are we magnetically drawn to each other? Can we sustain this? If it’s gone, what else is out there?
Concrete examples: A heat between you and another that registers as sexual, a sense of addiction or obsession, possession, turning off most people to attract the one that likes your scent.

I also wouldn't say predatory lust I would call it primal because they don’t know Jack about each other. Here’s the link to the website in case you get curious. Not sure how accurate it is but it does explain why my dog keeps humping her stuffed animals (being silly there) https://www.enneagrammer.com/the-three-instincts
He is either 1/2 vampire or a vampire killed someone he loved. I wish I could buy a hardcopy of this manga to add to my book collection. Off the chain!