喜 (Hei) centers on the life of Ah Hei (whose name literally translates as "joy" in Cantonese). Having been neglected by his parents, Ah Hei is forced to work and study in order to support himself and his older sister, Ah Ting - who suffers from what looks like a mild form of mental disability. Over the years, Ah Hei has kept Ah Ting close to his side, giving her food, shelter, care, and by his own definition, joy - all these by making sure she stays home at all times.

Yet the day comes when "joy" knocks on Ah Ting's door, and Ah Hei is forced to reevaluate his ways and in doing so, uncover the true meaning of joy.