Mariel, a young human girl with fragile health, resides in a remote mountain house between Switzerland and France for recovery. Her condition initially isolates her indoors until she encounters Memole, a tiny alien being.

She experiences profound loss: her mother is deceased, and her father remains often absent due to distant work, leaving her under the strict care of housekeeper Penelope. This isolation breaks when Memole’s tears revive Mariel from a near-fatal health crisis, forging an inseparable, life-sustaining bond between them.

Her character evolves through external relationships. She befriends Oscar, a boy sharing her fascination with the extraordinary, sparking romantic feelings. Simultaneously, she endures bullying from Grace, a wealthy classmate at their art academy. Grace’s jealousy over Oscar’s attention escalates into targeted cruelty and social ostracization. After Grace suffers an accident causing memory loss, Mariel initially assists with insincere care, detected by Grace. This experience catalyzes Mariel’s growth toward genuine empathy and forgiveness, reconciling their friendship. Mariel later mediates understanding between Oscar and Grace regarding their shared history.

Musically gifted, Mariel’s piano playing first attracts Memole and reflects her refined upbringing. She becomes a trusted human confidante to the stranded Riruru aliens beyond Memole, safeguarding their secret alongside Oscar and eventually Grace after Grace discovers the truth.

In the OVA *Marielle no Hōsekibako*, Mariel’s recollections of adventures with Memole frame the narrative while she remains in the mountains. The series concludes with Mariel’s health declining upon learning of Memole’s potential return to Riruru. Memole’s decision to stay ensures Mariel’s survival, cementing their interdependence.