Yashiro Hoshimiya is a mysterious figure first encountered by Makoto Niwa at a baseball game, initially mistaken for a Maekawa cosplayer. She presents herself as an alien esper, habitually wearing a makeshift spacesuit and sometimes adopting an artificial alien-like speech pattern. She insists her helmet contains latent esper abilities and rarely removes it.

Her distinctive appearance features medium-length platinum hair, blue eyes, and notably pale skin. She appears younger than the primary cast, often perceived with an unearthly beauty, her spacesuit serving as her most recognizable trait.

Personality-wise, she exhibits a childlike and stubborn demeanor, fiercely clinging to her claims about aliens and the supernatural. She snaps easily when Makoto openly mocks or questions her origins or powers, mirroring Erio Tōwa's initial fixation on extraterrestrial themes.

Background details remain sparse, with rumors suggesting she may be a runaway, contributing to her elusive presence. Concrete information about her origins, family, or past is absent.

The narrative subtly implies genuine supernatural capabilities, notably when she seemingly prevents a meteorite from striking Makoto, though the mechanics remain ambiguous. Her role in the OVA episode directly challenges Makoto's skepticism, conclusively demonstrating her powers, though their nature and extent remain unexplored.

No significant character development occurs across any media. She maintains a consistent belief in her alien-esper identity, and her interactions don't alter her core behavior or goals.