Jiruo is an instructor at Beruchoro Orphanage. Jiruo is a Moon/Purple Whistle, putting him one rank below Black Whistles and allowing him to be an instructor for future cave-raiders. Jiruo's mentor was the legendary White Whistle, Lyza The Annihilator, and has known Riko since she was a toddler.

Jiruo is a competent and strict instructor, never allowing the eager Red Whistle Riko to exceed the depth allowed by her experience. When the children break the rules or behave unruly, Jiruo will knock them on the top of the head to put them back in line. Despite his role as instructor, Jiruo cares for the children at the orphanage and is concerned for their safety, protecting them from the horrors of the Abyss as best as he can.