I’ve used a Thinblood as a guest star in an ongoing chronicle. I have a player who doesn’t really do long-haul stories (she’s very good, but she doesn’t like games that turn into homework: short, committed arcs are her thing). Her character is a chaotic Gen Z gremlin, connected to the PCs’ Mawla figure (as far as they’re aware IC, she’s his biological daughter and also his childe, only one of which is actually true), and we unleash her on the story whenever we need a session’s breathing room from the Revised-style machinations that take up much of our attention, or need to be dragged down to Planet V5 for some street level problems on the Rack.
It works because a) the Thinblood is connected to something the players have put coterie dots into: they’re invested in Sorcha’s da, so they’re invested in her, and b) because it gives the players someone who’s even more baby than their characters and needs looking after. It helps that c) she has Resources, Looks and a Discipline Affinity: at the start of our chronicle the PCs had two dots in Resources between the three of them and no in-house Oblivion. There’s a strong Hecata presence in the city and none of my original players were playing one, so having a friend who can clue them in to Spooky Goings On is really handy.
I think if you have a similar situation – a player who wants to commit something different to the game and doesn’t necessarily care about the long haul – this kind of occasional guest character works well, and that’s probably the best way to integrate a lone Thinblood (unless you’ve decided to pick a Merit package that lets them act like a less sycophantic ghoul, with capacity to operate in daylight: that can also be fun, but the player still needs to like doing solo scenes and the group dynamic needs to be comfortable with that).
When I was building this chronicle I also seeded a few other thinblood characters (four, plus this one who became a guest PC) and a thinblood-focused plot hook or two, in case the players wanted to give an all-thinblood chronicle a try. The specific story hooks I went for were the Bahari cult (for reasons that don’t necessarily summarise well – how long are you here for conversations about the Last Daughter of Eve, Lilith bullshit, and creative interpretations of the Gehenna canon?) and the Ashe conspiracy introduced through Chicago by Night (making drugs out of vampires, which resonates with both Thin-Blood Alchemy’s use of the body as crucible and the idea of thin-bloods as disposable citizens, tolerated but not valued, nobody caring if they live or die as long as they don’t bring the hammer down on any real Kindred).
I think to make them work you need to either go into Alchemy or a Discipline Affinity. Not both, but certainly one or the other. This isn’t so much a mechanical problem as a thematic one. Justin Achilli once told me that the supernatural powers in the players’ hands are a key element: without it, Vampire is just Mad Men, horrible people doing horrible things to each other for boring reasons. It’s feeding and the blood bond and Disciplines that introduce those lurid, monstrous, capital-G Gothic elements and elevate the game into passion play, and characters without those elements feel a bit… off-message, for Vampire.
One might argue that the thinblood “daywalker” who can fulfil the ghoul niche is a kind of double-negative version of this, rich and strange by their sheer contrast to other vampires, and I think if your table focuses heavily on vampires and vampire society then the thinblood can be a ray of light in the midst of all that. A touchstone with a little t – although now I want to make a Thinblood the focus of a Coterie Type, in the same way that locations or slumbering elders might be. Time to break out that Last Daughter of Eve concept again…
I’d also say it helps to “theory craft” every character in the context of a Session Zero in which you establish what the chronicle’s going to be like, roughly where the arcs are going to go, what dramatic (or tactical) role everyone’s going to take on. Vampire is in my opinion a writer’s room, not a guessing game – it works best when everyone playing is contributing to the makeup of the story, when information is fairly open at the table, and when “what’s going to happen” is less important than “how we’re going to feel about it and deal with it.” Every element of a character from Discipline spreads to Merits and Flaws to Predator Type is a potential contribution to that emergent drama. Thinbloods are no different.
In particular you want to look at what the Thinblood Merits and Flaws enable and complicate, whether they play along the same sectarian lines (good for fitting a Thinblood into a group of full Kindred) or whether they’re all pulling in different ways (good for fostering conflict within a Thinblood group).
You’ll also need to think about feeding. Thinbloods don’t have a Predator Type, and so they don’t have the raw dots in Merits, Abilities and specialities that enable easy feeding. It’s harder for them to just tamp down on the Hunger, which means they’re going to need help, or they’re going to need their consequences managed. In either case, expect feeding to be even more significant than normal, and accidents to be more common.
Bottom line: I think a Thinblood or two can play a role in your proper Kindred chronicle if the players’ interests and preferences create the right space for them. I think an all-Thinblood chronicle is interesting if you want to back away from what classical Vampire is about and really focus on Your Little Guys and how they make it night to night, with both the proper Kindred and the threat of the Second Inquisition as these looming threats they don’t really understand. It would also be fun, maybe, to experiment with different paradigms for vampirism by not having any ‘true’ Kindred around at all – that’d be a neat way to run a lore-agnostic or post-Gehenna chronicle, although by that stage you’re not so much playing Vampire: the Masquerade as using its rules to do your own thing.