Like all Padjal he has two thin horns growing from his head. He has a slightly darker skin tone than the other known Padjal, and darker, shorter hair. His eyes are pink.
Not of the prestigious Senna family, and not Stillglade Fane's Guildmaster, O-App appears as casual as any normal child, wearing a short-sleeved shirt and shorts. However, like all Padjal he is much older and wiser than he looks, and respected throughout Gridania as a valued bridge between mankind and Elemental.
O-App-Pesi mainly appears in a quest line surrounding the primal Odin, who has been stalking the forests of the Black Shroud since the Calamity, always returning some time after his defeat. In the final quest, "Fear and Odin in the Shroud," he draws Odin to Urth's Fount in hopes of better researching the primal's unusual recurrence. After he is defeated by adventurers in a trial, E-Sumi-Yan discovers the Zantetsuken has abnormally high amounts of aetheric energy. They conclude that "Odin" is actually a host for the sword itself. Just then, Bowlord Lewin arrives informing them that the Zantetsuken had been stolen by one of his men. The Padjal conclude the man's soul was taken by the blade to become Odin anew.