Jiruo possesses white hair and bright blue eyes, presenting as a young man of average height usually dressed in standard delver gear. He is nearly always frowning. A Moon Whistle delver, he serves as an instructor at Belchero Orphanage in Orth, overseeing the children's upbringing and well-being. Students call him "Leader," and he is approximately 20 years old.

Exhibiting a serious, stern demeanor often perceived as cold, this attitude stems from prioritizing student safety and his teaching responsibilities. Despite his strict exterior, he displays perceptiveness and compassion through insightful advice and support, maintaining confidentiality when necessary—such as protecting Riko's identity as Lyza's child.

His history includes apprenticeship under the legendary White Whistle Lyza "The Annihilator." As a Red Whistle, Lyza entrusted him with guarding Riko and her origins before her final dive. After Riko's birth in the Abyss, Jiruo played a key role in her initial care upon reaching the surface.

During the Orth Arc, Jiruo enforced new delving rules for orphans and emphasized artifact surrender to fund the orphanage. He resisted Riko's requests to delve deeper initially but relented when she proposed proving her worth through valuable finds. When Riko and friends caused a blackout reviving Reg, Jiruo investigated but failed to locate Reg hidden nearby. He later accepted Reg into the orphanage when Reg posed as a homeless child.

At the Orth Resurrection Festival, Jiruo encouraged Riko to participate in her mother's honor. He revealed Riko's poor eyesight resulted from the Abyss's curse and disclosed details of her birth. He arranged Riko's access to Lyza's sealed letter at the Delver Guild, instructing Reg to accompany her. On Riko and Reg's departure day, Jiruo encountered Reg patrolling the area and permitted him to leave despite Riko's absence. He later pursued them after providing a head start, leaving a warning letter in the Abyss's first layer.

In the Birthday-Death Disease Arc, Jiruo met Mio to examine the ailing Kiyui and accompanied them to the Caravan Fleet. He witnessed Kiyui's unexplained recovery and later traveled to Seeker Camp with foreign goods to confer with Ozen. They discussed superstitions surrounding the "Birthday-Death Disease" and praying skeletons. Ozen noted Jiruo's resemblance to Lyza during their talk. Later, while traversing Orth's slums, Ozen informed him of recurring twin births and introduced a limbless survivor of the spreading curse.

Holding authority at Belchero Orphanage, Jiruo supervises the orphans and leverages his Moon Whistle delving expertise to instruct apprentices.