A junior disciple of the Gusu Lan Sect. Born Wen Yuan, he's the last remaining blood descendant of the now-extinct Qishan Wen Sect. He was one of the Wen clan remnants taken in by Wei Wuxian shortly before his death, but he lost his home for a second time in the first siege of the Burial Mounds.

Discovered by an injured Lan Wangji who came searching for Wei Wuxian's remains in the aftermath, the then-three-year-old boy fell into a high fever and lost all memories of his past. He was then re-named to Lan Yuan and later presumably given the courtesy name Sizhui in the same year that Wei Wuxian returned to the living world.