Lee Seokmin, an energetic and kind-hearted university student, finds himself falling deeply for Joshua Hong, a reserved and gentle senior. Joshua, who has always carried an air of mystery, begins to reciprocate Seokmin's affection, and the two quickly become close. However, just as their relationship starts to blossom, Joshua begins to distance himself.
Unbeknownst to Seokmin, Joshua has been diagnosed with a terminal illness; an ailment that he has been silently battling. Joshua, who is uncertain about his future, fears burdening Seokmin with the uncertainty of his condition. Though deeply in love, he begins to push Seokmin away, thinking it's for the best.
Seokmin, confused and hurt by Joshua's sudden coldness, refuses to give up. He notices the cracks in Joshua's armor and becomes determined to understand what's going on. As he uncovers the truth about Joshua's illness, Seokmin faces the heart-wrenching decision of whether to stay by Joshua's side, despite the unknowns, or let him go.