Oseam follows two orphans, Ga-mi and her younger brother Gil-son. Ga-mi is a gentle and reserved blind girl, while Gil-son is hyperactive and often gets into mischief. The two seek refuge at a Mahayana Buddhist temple, helping with the chores, as they cope with the loss of their mother and home several years ago due to a fire accident, which is also where Ga-mi lost her sight. Gil-son, too young to understand, still believes they will find their mother someday as Ga-mi has never told him she died in the fire. After Ga-mi tells him of how their mother visited her in her dreams, Gil-son accompanies one of the monks on a pilgrimage up the mountain for the winter hoping that if he can "open his inner eye" he will be able to see her again, too.
The movie is very slowly paced, often quite slice-of-life in its approach, though dotted with moments of flashback and briefly intense scenes. A lot of emphasis is placed on the characters, particularly the orphans.