Souji Jikukawa is the president of the student council and the puzzle club of Root Academy. He is also a member of the POG's "Section φ(Phi)", Japanese branch. Souji holds the title of "Newton" and he is a giver called "Minotaur" but nobody, except the headmaster, knows about this.
Souji appears as a normal high school student, with longish brown hair and green eyes. He is always seen wearing the Root Academy uniform.
Souji Jikukawa is a rather secretive person, keeping many things from Kaito and his friends. Despite that, he appears aloof and friendly and is popular among students. He also cares about the well-being of his underclassmen and guides them.
Souji has a complex about not being able to become a Phi Brain Child. However, he takes pride in having talent as both a Giver and a Solver. Since the time when he was a member of "Section φ(Phi)", he was good at gathering information.
Jikukawa likes apple juice and he is usually seen drinking boxed juice. Kaito also remarks that it is strange for him to drink anything else.
Jikukawa is firstly seen as Minotaur, a mysterious person who guides Kaito to the Armband of Orpheus.
In the second season he decides to leave the student council and puzzle club because Orpheus Order asks him to join them, since he is good as both solver and giver. They give him a fake ring and after that Souji challenges Kaito to a puzzle, under effect of the Orpheus Ring.
Jikukawa's family is very rich and his parents are both POG members. Because of that his future as a giver is bright, but this isn't the reason why he decided to join in the POG. His reason reason was that he wanted to become a Phi Brain Child, but he wasn't accepted by the Orpheus Ring, so seeing that the Ring had accepted Kaito he put his dream, his hopes and his ambition in him and he decided to protect him and help him.
In season 3, after his admission to Root University, he joins POG officially.
- His name is a pun on Jigsaw Puzzle ("Jigusoo Pazuru" in Japanese)
- His habit of drinking apple juice is linked to his title "Newton", based on the story about Isaac Newton seeing an apple fall from a tree which is said to have become the inspiration for his theory of gravitation