Starting brainstorming work for my game focusing on playing witches in a coven. Them game’s main schtick (one of them) is going to be about the threads that bind people together; the closer people are the more strongly bound they are together in the web of fate, and the easier they are to impact with magic by someone strongly interwoven with them. This means those with virtually no ties to a character will be nigh immune to being impacted by their magic.
There will be ways to create temporary threads to make weaving spells possible (this might be playbook specific, or be things like having blood, hair, etc… from a person).
Thing is though, this opens up the real meat of the game to be more or less a weird soap opera about all the drama that goes on due to the relationships that bind characters (PCs to each other and to NPCs) together, so those need to be rich and fleshed out in some way. I’m not sure what the best way to start off rich “beginning histories” with important ties that bind are. Naturally, characters can all be part of a coven, they can be family too. I’m debating even having the coven be a sort of “third character” that all PCs share in a way and build before they build their individual characters. But, I’m torn on if starting off relationships should be left as “hey, you can kinda build these however you want, but here’s some help to get you started”, or “your playbooks define your starting threads or at least give you some specific options to start with”.
Starting threads (or at least suggestions) sounds as good a solution as any to me. A lot of PbtA games have suggested bonds/Hx/relations, but most seem pretty light, too easily disentangled for your purposes. I remember Monster of the Week actually started two of my players’ characters ended up being sisters, though (much to one player’s surprise!) just based on the options for starting relationships. I know other games love to use the “saved my life” thing too. Stuff like that is hard to shrug off, maybe more useful for your purposes.
PBTA games tend to lean on a small handful of pointed questions at character creation — see Monsterhearts for a good example.
Just brainstorming now, other options might include a GM move like ‘start, end, or reveal a relationship’ or something; or maybe a player-facing move that triggers whenever they try to take downtime and stirs up drama as a result. Or you could make that a start or end of session move.