TEMPE, Ariz. — D. J. Foster, Arizona State’s star running back, has a tattoo above his heart with “Sweet Dreams” inscribed below the smiling face of his sister, Jennifer.

On Thursday night, when the No. 15 Sun Devils host No. 11 U.C.L.A. in a matchup of undefeated Pacific-12 teams, one of the last things Foster will see before running onto the field is a laminated picture of Jennifer on the door of his locker.

She died of an accidental drug overdose five years ago.

“Every time before the game, during the game, I’m always thinking about her constantly,” Foster said. “When I’m having problems in my life, I’m always talking to her and praying. She’s looking over me and having my back. She’s my guardian angel.”

Jennifer, who was four years older and was Foster’s only sibling, attended most of his football and basketball games, although she told him there was more to life than sports. Ruth Foster, their mother, recalled that Jennifer and D. J. sometimes stayed up talking until 2 a.m.