Julian has dark brown eyes, brown hair, and tanned skin. He wears a grey jacket over a black T-shirt.
Autumn is Julian's ex-girlfriend. They split up with a year prior to the game's timeline. The two are on talking terms, though while he shows to still have feelings for Autumn, it is unclear how she feels about him. They share an awkward kiss in the final chapter of Book 2. In an option in Book 3, Chapter 4, you can get Autumn to dance with him.
You and Julian have an easygoing friendship in Book 1, but can be closer if your character chooses to play football alongside him. In Book 2, if you choose to do basketball, the friendship grows stronger. In Book 2, Chapter 14 you and Julian kiss in a game of spin the bottle. Both of you remark how neither is such a bad kisser.
Bethany finds him "cute" and openly flirts with him in the cafeteria in Book 3, Chapter 2. She is later disappointed when she hears that he has a thing for Autumn, but later moves on.
Julian and Max have been playing together at Hearst, but the former hates the latter's attitude to him and others as well as becoming football captain because of his father being the principal of Hearst. This enmity continued even after Julian's transfer to Berry High, when Max mocked Julian during a basketball match and falsely accused him of favoritism during baseball tryouts. Upon graduation and the revelation that Julian and Max will attend rival universities, the former laments that their rivalry will continue beyond high school.
- Julian is one of the few characters that originate from Pixelberry's High School Story app.
- In the original High School Story app, he has a sister named Hope, but she has yet to be mentioned by name (or to physically appear) in any of the books.
- Though, during prom in High School Story, Book 3, he does mention a sister, but it is unclear if this is Hope, or another one altogether.
- He was originally at Hearst High, before the series.
- In Spanish, "Castillo" translates to "Castle."
- He has a football scholarship to Ohio State, once again becoming rivals with Max.