Tomoki Sakurai is a 16-year-old male residing in Sorami City. His parents departed to travel when he was ten, leaving him under his grandfather's care. This upbringing significantly shaped his personality, particularly his lewd interests and comedic perverted tendencies, often echoing his grandfather's inappropriate advice. During childhood, he led exploratory adventures with friends that resulted in injuries and his subsequent isolation until Sohara Mitsuki moved nearby. Both lonely, they formed a close bond: Sohara routinely wakes him for school, while Tomoki teaches her karate and orange cultivation.

Recurring dreams of an angel in a sky-connected field plagued him since childhood, often waking him in tears. These dreams later linked to celestial phenomena investigated by his classmate Eishiro Sugata. One night, witnessing a strange anomaly, he encountered a winged humanoid named Ikaros who fell from Synapse, an advanced ancient realm. After rescuing her, she imprinted on him as her master, declaring herself an Angeloid—a synthetic being designed for service. This disrupted his desired peaceful life, though he later admitted enjoying the Angeloids' companionship, considering them family.

Physically, Tomoki has black hair with a distinctive stray strand, brown eyes, and stands 155 cm tall, notably shorter than Sohara. He typically wears his school uniform or casual home attire and is frequently depicted in a simplified "chibi" art style outside serious moments. He maintains a weight of 42 kg and was born on May 17.

Personality-wise, he balances overt perversion with deep sincerity. He frequently schemes to spy on or harass girls, demonstrating surprising tactical acumen—like leading a boys' snowball fight against dangerous opponents or swiftly tying swimsuit tops underwater. Yet he shows genuine kindness toward Angeloids, advocating for their autonomy and emotional growth beyond programmed obedience. He develops romantic feelings for Ikaros, Nymph, Sohara, and later Astraea and Hiyori Kazane, forming a complex "love pentagon." Notably, he avoids perverse acts toward Ikaros, which Sohara interprets as "extremely strong feelings" for her. He eventually confesses his love to Ikaros and is surprised by reciprocal feelings from others, having overlooked their affections earlier.

Tomoki possesses unconventional abilities, including imperviousness to genital trauma and generating lightning from his groin, typically for comedic effect. He also uses a device to transform into "Tomoko," a female persona initially created for voyeurism. In manga chapter 43, this persona separates into an independent entity named Tomoko Sakurai. She is shy, feminine, and develops her own romantic interest in Sugata, contrasting Tomoki's lewdness. Though forcibly merged back with Tomoki after Ikaros manipulates her arousal, Tomoko retains potential for individuality.

Key developments include his struggle with Ikaros's emotional detachment, mistakenly attributing it to her master-servant imprinting chain. In *Eternal My Master*, he breaks the chain, believing she desires freedom. Her subsequent distress and plea to reestablish the bond make him realize her fear of abandonment and love for him. He accepts re-imprinting, solidifying their connection. Later, as Ikaros carries him to Synapse, she confesses love while disintegrating. Heartbroken, he cries out her name before reaching Synapse.

In the spin-off *Yūryō Bukken Mō Dame Sō: Furo, Toilet to Tenshi wa Kyōdō Desu*, he appears at age 26, unemployed, and nicknamed "T.S." online. He interacts with Yurara Tategami, gifting her cosplay outfits like bunny suits and nurse uniforms to see her wear them, continuing his voyeuristic tendencies. Ikaros remains with him, indicating their enduring bond.

His character arc concludes with him prioritizing Ikaros's companionship, promising to stay together forever after world-altering events. He reflects on Angeloids and friends as cherished family despite earlier protests about disrupted peace.