Yu Ominae (御神苗優 Ominae Yū) is the main leading protagonist, stationed at ARCAM's Japanese branch.
He is also the former member of COSMOS. He is known for being a high school delinquent to his teachers and classmates, he is secretly a special Spriggan agent for the international conglomerate ARCAM Corporation. As such, Yu gets thrown into missions in and out of Japan when out-of-place artifacts are involved in a mission.
Yu has short spiked black hair with dark brown eyes.
Yu is called upon by ARCAM to conduct black ops for the company, which results in several disruptions from his studies. His most dangerous mission to date was to be deployed into the South Pole in order to eliminate the South Pole Shrine. After the successful operation to eliminate the rampaging Fire Snakes from the South Pole Shrine and defeating Markson's Trident forces in the South Pole, Yu was seen attending college after graduating from his high school. He is still posted at ARCAM's Japanese branch, attending to a mission in Mexico to secure the Gold Statue of Pachacamac and secure the safety of his classmate, Nanako Kondo.
Yu and Yamamoto are teammates at the first appearance. As Yu's supervisor, he has a duty to find out various OOParts that research team found at chosen region.
Yu and Rie are childhood friends.
Although teamed up as well-known partner, Yu and Jean considered as a rival.
Her first appearance that involved him made himself annoyed by her actions. Yu called Yoshino herself as low ranked artifact thief.
As his mentor, Oboro also tests his developing skills against Yu after fought against Jean. Unfortunately Oboro defeated by him by single punch. He also realized that Oboro did less training after defeated.
Yu meets his adoptive father and uncle somewhere in the Native American forest where Jean easily trapped by his hand-made trap.
His relationship with his adoptive sister and cousin also shown when she announces Henry Garnum.
Despite Yu and Precup are teammates, he was disgusted when Yu called him "gramps" that makes him easily annoyed.
In his daily attire, Yu wears gakuran high school uniform (where in summer he didn't use his gakuran coat) when in his school duty. He also wears a pair of various casual t-shirt (with sleeve in summer session or full sleeved in winter session) with fabric trousers or jeans in his off day or his duty in Japan. In his military duty, he wears one set of Orichalcon armored muscle suit, made by Dr. Mayzel.
Yu's personality is bravery, hot-headed and impatient teenager. Sometimes he also mischief and annoying (especially when facing Sasahara sisters) and has a worst habit in school where he always sleeping in the class that makes him got a worst score during test. However in his military duty as a Spriggan, he is one of the best in combat (both long-ranged and short-ranged). His passions in fighting against the strongest enemy also makes him more aggressive.