The brother of Navarre, Gaston is one of Nanashi's allies.
Gaston is an 18 year-old samurai from the Eastern Kingdom of Mikado who has received orders to defeat the faction known as the Divine Powers. He hates his brother Navarre for sullying their family's name.
All of Gaston's skills are physical and his Partner Awakening passive grants the equivalent to High Phys Pleroma. Gaston is the only partner with high physical strength when compared to the entire team. Gaston will randomly interrupt Nanashi and his demons and perform his own attacks, effectively using up the their turn icons. This property can be useful in grinding relatively weak demons, but not so good in boss fight. As Gaston doesn't rely on his smartphone to battle, he can still provide support while the Tokugawa Mandala is active. Because he wields the Spear of Michael for most of the game, Gaston is capable of hitting Shesha's weakness and his actions will award the player with half-turns as if they had attacked Shesha's weakness themselves.
There is also a very unpleasant behavior of Gaston's AI: If all enemies repel physical attacks, Gaston will stay put during the partner's turn, but he will still interrupt the player's turn and the attack will result in the loss of all player turn icons or when his attack missed. The player will have to pay for it by losing a lot of turn icons.
When the party attempts to access the Cosmic Egg, Odin confronts them at its entrance. They do battle, and Odin offers Gaston his Gungnir should he be bested. After Odin's defeat, Gaston claims Gungnir for himself and his skill set changes, allowing all his attacks to pierce resistances. He also gains a new ultimate skill to be learned.
The Greek embroidery on the wrappings of Michael's spear roughly translate to "Archon Michael," with "archon" being the Greek word for "ruler." An archon is a servant of the Demiurge in gnosticism, who is tought to be the biblical YHVH.
In a similar fashion, the word "Gungnir" can be read in runes on the eponymous spear.
