When I planned out the characters for Astrid, I knew I wanted a group of core friends.  I also like threes, so I planned the characters in triads.

Astrid has two femaile friends at the start of the story– Valerie and Denise.  So Astrid, Valerie, and Denise form a triad.  Then Astrid has a boyfriend, Toby.  Toby’s best friend is Christopher.  Christopher is also super smart and competes with Astrid at school.  So Astrid Toby and Christoper for a triad.  Austin is the new kid in school and forms the third boy in the group– making a Toby, Christopher, Austin triad.

In addition, each of the characters relate to each other in different ways.  Austin has a special connection to Denise and especially Valerie, who are his first female friends.  Astrid and Toby both take Austin under their wings, in different ways.  And there is the second Valerie, which adds a whole ‘nother layer to the Astrid-Valerie relationship.