Gammon Sakanoue is portrayed as hot-tempered, competitive, and opportunistic. Unlike Kaito Daimon, who solves puzzles for the joy of it, Gammon often tackles puzzles for monetary gain, both to support himself and to provide for his younger sister, Miharu. He is also known under the alias “Chidousetsu,” a well-regarded puzzle writer who contributes to magazines.

He maintains a sharp rivalry with Kaito, frequently mocking him with nicknames such as “Bakaito” (a combination of “Kaito” and baka, meaning “idiot”) and “Freakaito.” Despite their antagonistic banter, the two share several similarities, including their fiery tempers and remarkable talent for solving puzzles. Gammon is recognized as a skilled Solver and Giver, and although considered a top candidate to become a full Phi Brain, he remains the only one who has yet to experience a vision of the future.

Beyond his rebellious appearance and brash attitude, Gammon cares deeply for Miharu, his younger sister, whose well-being is his primary motivation for pursuing puzzle-solving as a livelihood. He demonstrates responsibility in domestic life as well, often preparing meals for her since she is unable to cook. Gammon also appears to harbor feelings for Nonoha Itou, going so far as to enter a cross-dressing contest in an attempt to impress her.

Gammon Sakanoue is tall, with spiky red hair distinguished by two strands that hang down in the front, and gray eyes. His style contributes to his rebellious image; he is almost always seen wearing a leather jacket and pants, reinforcing his delinquent-like appearance. Combined with his rough way of speaking and mannerisms, this look makes him stand out from his peers.

In addition to his distinct fashion, Gammon is frequently associated with his motorcycle, which further complements his bold and rebellious persona.

Gammon Sakanoue grew up alongside his younger sister, Miharu, for whom he feels a strong sense of responsibility. With their circumstances requiring him to support the household, Gammon began solving puzzles for money, often taking on challenges set by the P.O.G. in hopes of winning rewards. At the same time, he gained recognition in the puzzle community as “Chidousetsu,” a pseudonym under which he published puzzles for magazines.

Despite his rough exterior and rebellious streak, his primary motivation has always been the well-being of Miharu. This sense of duty drives many of his decisions, from his puzzle-solving career to the lengths he is willing to go to secure financial stability for them both.

Kaito Daimon
Gammon considers Kaito his primary rival, frequently mocking him with nicknames such as “Bakaito” and “Freakaito.” While their competitive relationship is often antagonistic, it is also built on mutual respect, as both are highly talented Solvers. Over time, their rivalry evolves into a reluctant camaraderie, with Gammon often assisting Kaito despite his pride.

Nonoha Itou
Gammon harbors a crush on Nonoha, Kaito’s childhood friend. He occasionally attempts to impress her, including entering a cross-dressing contest to show her a different side of himself. Despite these efforts, his feelings are portrayed mostly as one-sided, as Nonoha’s primary focus remains on Kaito.

Miharu Sakanoue
Miharu is Gammon’s younger sister and the person he cares about most. Her well-being is his central motivation for puzzle solving, whether by competing for prize money or working under his alias as a puzzle creator. Gammon is protective of her and takes on domestic responsibilities, such as cooking, to ensure she is cared for.

The name Gammon is derived from the board game Backgammon, reflecting the series’ recurring theme of puzzles and games. His surname, Sakanoue (逆之上), is composed of saka (逆), meaning “inverted,” “reverse,” or “opposite”; no (之), meaning “this”; and ue (上), meaning “above” or “top.”