To heart: koishite shinitai (1999)

Tohko is living in 1999, and dreams of falling in love before the world supposedly ends in 2000. When she sees aspiring boxer Tokieda Yuji practicing in a park, she falls for him instantly. Unfortunately, in spite of her best efforts, Yuji doesn't see Tohko as a love interest, and is instead feeling his own unrequited love for Kaori, his boss at his part time job. But Tohko is determined to win Yuji, and never stops cheering him on in his dream to become a champion boxer. Will Tohko win Yuji's love?