I was going to just do this for Galar characters like the ask said, but then I realized I don’t have a list of all the related canon characters anywhere so I think I’ll include that as well, under a cut.
Galar
Kabu is Flannery’s uncle, which is something inspired by cute fanart of them together. Flannery’s father, Hoku, is Kabu’s identical twin brother and the two have a good relationship. Hoku’s very much a prankster though so whenever he visits his brother in Galar he has a habit of pretending to be him and doing weird/silly things, much to Kabu’s chagrin. Flannery couldn’t tell them apart until she was like 7.
Piers and Marnie are related to the Montfort family of Unova (which includes Grimsley and both sets of Unova protags). Their grandfather, Orpheus, was the twin brother of Calliope, Grimsley’s mother and the grandmother of the BW/BW2 protags. Meredith, Piers and Marnie’s mother, was the result of a fling Orpheus had, however, so this relationship doesn’t get discovered until after SwSh’s plot I don’t think. So this means that Piers and Marnie are the second cousins of Hilda, Hilbert, Nate, and Rosa, and the first cousins once removed of Grimsley, Diana (Hilda and Hilbert’s mom), and Harper (Nate & Rosa’s dad).
And now for a much briefer breakdown of the other relationships in this verse (in no particular order)!
- Blaine is Red and Leaf’s grandfather. Consequently, Red and Leaf are also siblings.
- Samuel Oak and Agatha are exes and had a son together, Thaddeus, who was born after they broke up. He was raised by Agatha and went on to become Morty’s father, meaning Morty is the half-cousin of Daisy and Green.
- Yellow & Lance are first cousins. (They’re also first-cousins with Nobunaga because Conquest is canon to L&L history but that’s a story for another day.)
- Bill is the cousin of the Kimono Girl sisters.
- Falkner and Will are half brothers. Will is also Lucian’s half brother, as his and Falkner’s mother had an affair with Argenta, Lucian’s mother (who was single at the time).
- Mars is Silver’s older sister and like him is Ariana and Giovanni’s kid.
- Jasmine is May and Max’s first cousin (her mother and Norman are siblings.)
- Archer and Proton are brothers.
- Hun is Tory Lund’s older half-brother.
- Vincent is Professor Elm’s son.
- Pierce & Tobias are brothers.
- Chase and Elaine are twins.
- Brendan is Wattson’s grandson (and Prof Birch is Wattson’s son.)
- Wally and Drew are first cousins.
- Clair is Kris/Crystal’s older sister.
- Winona and Wallace & Lisia are distant cousins.
- Maylene is Mira’s older sister.
- Zinnia is Sawyer’s first cousin once removed (aka Sawyer’s dad is her first cousin.)
- Tucker & Butler are twins and the older brothers of Courtney.
- Dawn is Looker’s daughter and Cyrus’s niece (Johanna is Cyrus’s older sister who ran away from home with her rookie Interpol bf.)
- Barry & Bianca are cousins.
- Verity and Cynthia are cousins.
- Ursula is Reggie & Paul’s cousin as well as Lila’s daughter (Reggie & Paul’s mother was Lila’s late sister.)
- Hilda & Hilbert are twins and the first cousins of Nate & Rosa who are also twins (it runs in the family). Grimsley is their uncle.
- Wikstrom & Darach are brothers.
- Volker and Elesa are siblings.
- Brycen is Pryce’s son.
- While this isn’t true in canon, Iris is Drayden’s blood-related granddaughter in L&L so I thought I’d mention it.
- Shauntal is Cosette’s older sister and the two of them are the daughters of Fantina and Juan, who are now divorced.
- Ghetsis has a whole ton of love children from various escapades so apart from N (who is his blood-related son in L&L) and Anthea & Concordia (adopted like in canon), he’s the father of Aaron, Sorrel, Curtis, and Sawyer (and Ginger but he’s a fankid.)
- Calem is Alain’s younger brother and the two of them are Sycamore’s nephews.
- Clay is Serena’s great uncle (aka Grace’s uncle).
- While this is a canon relationship, since Emma gets semi-officially adopted by Looker, she and Dawn consider each other sisters.
- Siebold is Korrina’s older brother.
- Mairin is Ramos’s granddaughter.
- Selene & Elio are twins.
Pokémon Legends & Legacies 