Swell Rec, older sister to Echo Rec, shares a home with him in the scrap-heap town of Liverchester, where she runs the Oasis bar. When Echo discovers an amnesiac girl named Mu near the garbage mountain, Swell welcomes Mu into their home, providing shelter and support as Mu recovers. After Mu resolves to leave Liverchester and uncover her past, Swell funds her journey yet assures her she may always return.

Swell acts as a protective, encouraging force for Echo, backing his dreams of exploring beyond Liverchester and his fascination with Players and Equipment. She serves as both sister and a stabilizing, parental figure in his life. Later, when Earless attacks and emerging Listeners threaten Liverchester's destruction, Swell remains in town, witnessing McGee’s efforts to raise the monument. Mu, appearing in spiritual form, urgently warns Swell to flee the impending danger.

Her interactions reveal a consistently calm, resilient demeanor. She adeptly manages confrontations at the Oasis, diffusing tensions when McGee and an associate threaten to damage the establishment, reinforcing her grounded, capable presence within Liverchester’s community.