Sōji Jikukawa holds the presidency of both Root Academy's student council and puzzle club. Initially a Solver known as "Newton," he failed to attain the status of Phi Brain Child in his freshman year, a failure that became a personal complex. The academy's headmaster later introduced him to P.O.G., where he now operates secretly as the Giver "Minotaur," an identity hidden from most students, including Kaito's group.

His wealthy parents are members of P.O.G., but his own decision to join stemmed from witnessing the Orpheus Ring accept Kaito. Placing his ambitions in Kaito, he guides the underclassman towards the Puzzle of God while covertly working within P.O.G., fueling his protective stance towards Kaito and others.

He maintains a friendly yet aloof demeanor, enjoying widespread student respect. Often seen smiling, his signature habit involves drinking boxed apple juice through a straw, a nod to his "Newton" title and the Isaac Newton anecdote. This secretive nature coexists with genuine concern for others.

During the second season, the Orpheus Order recruits him for his unique dual Solver-Giver talents. Accepting a fake Orpheus Ring subjects him to brainwashing, drastically altering his behavior. He challenges Kaito to deadly puzzles, resigns from his presidencies, and abandons his trademark apple juice in a pivotal confrontation.

Progressing in the third season after entering Root University, he officially joins P.O.G., utilizing his talent for information gathering honed during his earlier "Section φ(Phi)" membership.

His name functions as a pun for "jigsaw puzzle" ("Jigusō Pazuru" in Japanese). His consistent preference for apple juice serves as his character signature throughout appearances.