For Briar, her immediate best friends are naturally Rose and Oleana, they're her ride or dies and the people she talks the most every day. But she also has a couple of more people she considers close to her, like Grimsley, who's a childhood friend of hers (her dad and Grimsley's dad know each other); they kinda fell apart when Grimsley became a member of the Elite Four and Briar moved to Kalos for college, but after some years they started talking again and they became somewhat closer with the years.

Another important friend of hers is Jacq. They were classmates in Lumiose University since they were both studying to become biologists. Jacq means so much to Briar since he helped her with her scientific career, even if he's not aware of this. Not only for the mutual motivation during class, but also after graduating, Jacq was the one who helped Briar go to Paldea for a while to study engineering, that would become crucial to her career in the future. He's also the one who introduced Briar to Oleana, and the story speaks for itself.

Lastly, another character I'd like to add is Colress. I think they would meet in Alola and I like to think they became friends because they're both unhinged enough with their researches to understand each other LOL So that's how they clicked.