He first appeared in the second part of "Over a Barrel" where he had a terrible argument with his father. That's because Tuan's grades have slipped lately, he skipped school and he was late for dinner and that's because he was focusing more on the band than his education. Tina even argued with him because of it. But eventually after his Dad heard Tuan's music, they straighten things out.
His last appearance was in the series finale story arc "Attack of the Slime Monster" where he and Lenni practiced doing a gig for the Hurston Middle School senior prom. The time Tuan and Lenni spent together spawned an attraction on the part of Tuan, noticed by Tina. By the story arc's end, Lenni had begun to accept Tuan's personality, with which she had clashed before, and his attraction toward her. She then happily proceeded to agree to slow dance with him in the loft. He is last seen talking to Lenni at the graduation party for her, Jamal and Alex and then playing a game with some of her friends.