Saint Valentine appears only in the dreams of those who eat Hana Miyakoshi's toxic homemade chocolate, which induces near-death states. This spiritual entity interacts with these unconscious individuals as a guide during critical junctures.

He displays a cheerful, carefree attitude but reacts with sharp irritation when upset. Despite this, he shows genuine concern and readily shares wisdom. His primary connection is with Daisuke Higashida, whom he frequently meets in these dreams after Higashida repeatedly consumes Miyakoshi's chocolate. Valentine guides Higashida, using his energetic and creative nature to help him regain consciousness and confront his struggles.

He holds a distinct dislike for Miyakoshi, chiefly due to her violent tendencies, which persist even in dreams. Yet, he acknowledges a need to assist her, offering advice specifically aimed at improving her relationship with Higashida. His counsel to Miyakoshi centers on fostering better understanding and interaction between the pair.

His final manifestation occurs without Miyakoshi's chocolate as the trigger, coinciding with the moment Miyakoshi begins to recognize her romantic feelings for Higashida. This marks a turning point, facilitating the resolution of their complex dynamic shortly after. Valentine's role consistently involves mediating pivotal developments between Higashida and Miyakoshi through these dream interventions.