Syrup is a fairy delivery boy who transports letters anywhere alongside his partner, Mailpo. He transforms between a bird-like fairy form and a human identity, Amai Shiroh. His fairy form has tan feathers, green streaks on his head, and a red scarf. As Amai Shiroh, he appears as a boy with scruffy hair, an orange uniform, and a brown shirt, later evolving into an adult with ruffled hair, a light brown vest, and a beige long-sleeved shirt.

Suffering amnesia since arriving at the Palmier Kingdom, Syrup seeks the Rose Pact to access the Cure Rose Garden and recover his lost memories. His past reveals he was raised by Flora, the garden's guardian, who entrusted him with a delivery mission. An attack by Anacondy during this mission caused his memory loss. Distrusting Coco, whom he perceived as dishonest, he left the kingdom and worked for the organization Eternal while dreaming of the garden.

Initially distrustful and hostile, Syrup holds a strong grudge against Coco, avoiding him and Nuts. He questions his involvement with the Pretty Cure team but gradually forms trust and friendships, especially with Urara Kasugano (Cure Lemonade). Her kindness helps him overcome loneliness, inspiring him to learn music. He also bonds with Nozomi Yumehara over shared feelings of isolation. Syrup deeply reveres Flora as a maternal figure and is profoundly affected by her death. He combines straightforwardness and hard work with a notable love for pancakes, working at a school lunch cafe to satisfy this craving.

Tempted by lingering resentment towards Coco and Anacondy's promises about his past, Syrup betrays the team by stealing the Rose Pact. Memories of the Cures during the exchange with Eternal make him reject the deal. Witnessing the Cures defend him despite his betrayal solidifies his loyalty. After Eternal's defeat, he accepts Flora's death and becomes caretaker of the Cure Rose Garden.

In *Kibou no Chikara ~Otona Pretty Cure '23~*, Syrup tends the garden, observing a mysterious bud blossom into Nozomi's Time Flower. He supports the adult Cures by delivering letters, such as maintaining communication between Nozomi and Coco, and intervenes to protect others using his bird form for aerial rescues. His interactions with Urara deepen; he visits her during career struggles, admits her singing inspires the garden's roses to bloom, and learns guitar to collaborate on her music. He also transports Cure Lemonade into digital spaces to confront enemies.

The alias "Amai Shiroh" is a pun: "Amai" (甘井) means "sweet," referencing "Syrup," while "Shiroh" (シロー) uses katakana, partially reflecting the Japanese word for "white" (白). Karen Minazuki accidentally revealed this name publicly. Syrup frequently ends sentences with "~ropu!".