Kenji Seki suffered a life-threatening incident in childhood that plunged him into a coma. His childhood friend, Natsuki Suzuura, desperately used her innate psychic abilities to save him, traveling back in time to prevent the incident. While successful, this act permanently shattered her powers due to overexertion. This shared trauma forged a protective bond between them. Natsuki harbored deep, unspoken feelings for Kenji, stemming from this event. Their close relationship was reflected in their affectionate nicknames: she called him "Ken-chan," and he called her "Natsu."

Kenji lived with his grandfather and a younger sister. Limited details exist about his family life or daily activities during this period. Aware of Kenji's latent psychic potential, his grandfather deliberately sealed away these abilities, likely to protect him following the trauma or from future threats. This sealed power remained dormant until triggered much later. Kenji's known childhood centers solely on the pivotal events of his illness, Natsuki's sacrifice, and the sealing of his powers. These form the foundation explaining his bond with Natsuki, the origin of her powerlessness, and the source of his own significant, though initially suppressed, psychic abilities.