Jiroubou was from a Japanese Magus Family that practices Shugendō Magecraft, who were in turn a smaller branch family to a much older clan of Magi. Jiroubou's father, despite not being married, was noted to have fathered numerous sons, due to having been quite popular with women. With Jiroubou being noted to be among one of the younger sons, having many older brothers. Due to the sheer number of children he had, Jiroubou's father concluded that the best way to find a heir would be to have his sons compete with each other during the course of their upbringing together and pick the whoever showed the most promise as the heir.
Due to their chosen path of Shugendo, Jiroubou and his family would frequently spend their time in the wilderness physically training each other to increase their physical abilities due to the unique blend of Magecract and Religion Shugendo embodied. During this time, Jiroubou became particularly close to one of his older brothers, who was later shown to be the most innately talented out of the siblings and was thus then chosen by their father to be the inheritor to their Magic Crest.
Jiroubou himself had little interest in Magecraft and was fine with the arrangement. However several of his older brothers were not and instead developed immense jealousy over their brother being chosen as heir. This eventually caused them to secretly plot to team up together and kill him to claim the crest for themselves during the inheritance ceremony to pass on the Crest.
Jiroubou due to his disinterest in Magecraft, chose to skip out in attending the ceremony with the rest of his family and as such remained oblivious to his brother's plot. Eventually his older brothers attacked both his father and elder brother during the Succession Ceremony in order to claim the crest. However despite their numerical advantage and due to them being much less talented than their brother, they soon found themselves massacred and defeated by their brother and father. However despite defeating them, Jiroubou's elder brother had been gravely wounded during the battle and was burnt to near death by his siblings. And with their father dead and all of his other siblings killed in the crossfire, he immediately contacted Jiroubou to come and retrieve the crest from him before he could die and their families Crest lost with him.
Jiroubou immediately traveled to the temple where the ceremony was held, where after seeing his families mangled burnt corpses and the burnt remains of their battle, he finally located his elder brother, who during the course of the battle was reduced to a near death state due to having been burnt to near death by Tengue Flames. Half dead and only kept alive by the crest, Jiroubou Brother begged him to inherit the Crest himself as his final dying request to his younger brother, Jiroubou despite his reservation and reluctance agreed, and transplanted it into himself due to wanting to honor his brother's final wishes and pass on the Crest to his future descendants.
However due to the battle and his brother's body being severely burnt to near ashes by the Tengu Flames used by his siblings, the crest was noted to have taken serious, near irreversible damage. Thus, this lead Jiroubou to travel and approach Geryon Ashborn in order to repair and fine tune the crest. This however, unknowingly resulted in him also being implanted with the Ashborn family's crest and the remnants of Geryon son's mind into his own consciousness that began to gradually meld together with his own.
Jiroubou hits on every girl at Adra, but everyone else finds him offputting. That said, he's a reasonably nice guy otherwise.
Though he is unsuitably good natured for a magus, the fate he met in the Adra incident can be clearly seen in the story.
Lord El-Melloi II Case Files
case. Castle of Separation Adra
It is revealed that thanks to the Ashborne Magic Crest, Glannid Ashborn, the supposedly deceased son of Geryon Ashborn and actually Orlocke Caesarmund's son, is reborn through Jiroubou and in control of his body. Glannid was the villain behind the incident at the Castle of Separation, and after his defeat efforts are taken to help Jiroubou become his old self again.
case. Grand Resolution
He is one of the people who show up to accompany Waver and Gray in their journey through the Spiritual Tomb of Albion and help them catch up to Doctor Heartless, using the Rail Zeppelin to get there. He comes back with a Mystic Eye beneath his eyepatch and a prosthetic arm made from a ghost root.
After the end of the series, he appeals to a number of magic organizations in order to help save Rosalind.
Seigen is a practitioner of Shugendou magecraft and is capable of the well-known Raven or Tengu Flight technique. With this he is shown to be able to casually jump several meters in the air in avoidance of an attack. The Shugendou he practices is originally something optimized for the Far East, but thanks to his ancestors’ admiration for the West, he also possesses a Magic Crest.
With the Mystic Eye beneath his eyepatch and his prosthetic arm made from a ghost root, he has an unnecessarily high amount of protagonist power.
Later upon being revealed to be the "reincarnation" of Glannid Ashborn, Jiroubu had inherited the Ashborn's Magic Crest and with it, the Ashborne's Mage craft of affecting, changing, stealing and "tuning" the Magic Crests of other Magus Families. He later displayed the ability to actually "eat" these Magic Crests as well, due to "craving" them because they had looked "delicious" to him.
Also due to inheriting the Ashborne magic crest, Jiroubou had also inherited the ability to command the Adra Castle's guardian familiar to do his bidding.
- Lord El-Melloi II Case Files Volume 1 - "case. Adra Castle Separation"
 Lord El-Melloi II Case Files material - Encyclopedia: Tokitou Jiroubou Seigen [Person], p.103-104
Tokitou Jiroubou Seigen [Person]
One of the magi invited to Adra, the Castle of Separation.
The Shugendou he practices is originally something optimized for the Far East, but thanks to his ancestors’ admiration for the West, he also possesses a Magic Crest. Though he is unsuitably good natured for a magus, the fate he met in the Adra incident can be clearly seen in the story.
Though it was thought he would leave the stage at that point, he made a brilliant return in the Grand Roll incident. With the Mystic Eye beneath his eyepatch and his prosthetic arm made from a ghost root, he has an unnecessarily high amount of protagonist power. After inheriting the magecraft of the Castle of Separation and taking care of Rosalind, the younger sister of his departed friend Heine, this author couldn’t help but apologize constantly while writing. “You’re such a good guy. Sorry for putting you through all this.”
After the conclusion of Case Files, he appealed to a number of magic organizations in order to help save Rosalind, but that’s a story for another time.
- Lord El-Melloi II Case Files Volume 9: case. Grand Resolution (Middle)
- Lord El-Melloi II Case Files Volume 10: case. Grand Resolution (Lower)