Memoru hails from the planet Riruru, one of 245 inhabitants stranded on Earth after their spaceship crashed. Her people are tiny, small enough to stand on a human palm, and possess gnome-like qualities. This crash forced adaptation despite their significant physical differences from humans.

Memoru wears a signature pointed hat, a key part of her distinct look. Her minuscule stature creates a stark contrast with the vast human world she explores. Personality-wise, Memoru is bold and adventurous, often described as reckless for venturing into human environments despite dangers. This fearlessness coexists with deep empathy, especially in her emotional responses to others' suffering.

Her most significant bond forms with Marielle, a human girl in a remote house near mountains between Switzerland and France. Marielle's fragile health initially confined her indoors, creating a shared experience of isolation with Memoru. Drawn by Marielle's piano music, Memoru discovered her. A pivotal moment occurred when Marielle's critical condition moved Memoru to tears; one tear falling on Marielle's lips contributed to her recovery, becoming foundational to their evolving friendship through shared experiences.

Memoru also connects within her community, interacting with fellow Riruru inhabitants Popitu, Rupangu, and Pi. Her companionship extends to woodland creatures, notably an owl named Bo-bo who transports her, highlighting her integration into Earth's ecosystems while maintaining her alien origins.

The dynamic between Memoru and Marielle unfolds through both present interactions and remembered adventures. Narration sometimes frames their experiences through Marielle's recollections during her convalescence, underscoring how their cross-species friendship shapes both characters' understanding of trust and mutual support. Memoru's presence consistently influences Marielle's worldview, just as human experiences expand Memoru's perspective.