Kagari embodies Earth's will within the Rewrite universe, known as the "Key" for her power to initiate planetary salvation—a process that would eradicate humanity to restore planetary energy. Her existence is intrinsically linked to Earth's lifecycle, emerging from biological hotspots in forests. She initially displays limited emotional expression and communication, observing humans with detached curiosity. Her interactions with Kotarou Tennouji involve nocturnal visits where she hides under his bed or bites his arm; her ghost-like invisibility to others makes these encounters seem haunting. Her role diverges across Rewrite routes. In Kotori's route, she protects Kotarou from threats and sings the Song of Destruction before being fatally shot. In Akane's route, she is forcibly used to enact salvation and is bisected by Kotarou. The Terra route depicts her collaborating with Kotarou to find humanity's "good memories," culminating in their fusion into an orb of light within a giant tree to halt ecological collapse. This act spares humanity but triggers an ice age beyond Kazamatsuri. An anime-original route shows her personality shifting after amnesia caused by a meteorite strike, leading her to seek Kotarou's help in rediscovering her identity. Within Kaginado, Kagari appears as a super-deformed chibi character alongside other Key franchise protagonists. She retains her original silver hair, lilac eyes, and red ribbons design while adapting to the series' comedic and meta tone. In Episode 1, she floats in space with Kotarou and the Rewrite heroines, waving from the Moon as they drift past. Her limited dialogue and stoic demeanor contrast with surrounding absurdity, such as passively observing chaotic school events or cross-franchise interactions. Episodes 19–20 highlight parallels with Tenshi (Kanade Tachibana) from Angel Beats!, noting their visual similarities and voice modulation traits within the Kaginado universe. Kagari's inclusion often serves as a referential joke to her apocalyptic origins, featuring her deadpan presence during mundane academy activities or fourth-wall-breaking gags about her power over world destruction. Her background is acknowledged but serves primarily as a fixture within the crossover's ensemble cast.