Emi Kojima serves as the human alias for Septem, a being originating from the magical world of Evergreen. Her true identity is Septem, and she adopts the persona of transfer student Emi Kojima attending Chihaya Hiiragi's school. Septem partners with Bergamot, Chihaya's father, to shield Chihaya from threats posed by antagonists Fennel and Calendula. Bergamot's attraction to Septem arises from her resemblance to his deceased wife, Emi Hiiragi, though Septem's feelings for him are genuine.

Within the anime television series, Septem initially appears distant and unsociable. Her dynamic with Chihaya shifts significantly after Chihaya rescues her during a monster attack, leading Septem to express gratitude and fostering a growing connection. This development extends to social settings, such as a sleepover at Sayaka's mansion, where Septem demonstrates increased openness to forming friendships.

Contrasting her anime portrayal, the original OVA series depicts Septem as a villainess. The *Summer Camp* OVA special features her participating in a beach trip. During this storyline, classmate Nami Minami falls under the influence of the "Netherworld Tree" following intensified unrequited feelings for Natsuki; Septem's direct involvement in resolving this incident lacks explicit detail.