Suguru Ōmi serves as a Guardian protecting the Tamayori Princess, Tamaki Kasuga. Descended from the giant snake orochi, his lineage grants control over water and the ability to create powerful defensive barriers and seals. Standing 185 cm tall, he has distinctive dark green hair often tied in a ponytail, amber eyes, and typically wears glasses.

Ōmi presents a consistently polite, reliable, and approachable demeanor, frequently smiling. This masks deeper complexities rooted in his past: his mother, a former Tamayori Princess, was sacrificed to maintain the seal on the demonic sword Onikirimaru. This fuels his opposition to sacrificial traditions and intensifies his protective instincts, contributing to a guarded nature. He rarely places full trust in others due to perceived threats to the Princess and displays ruthlessness when outsiders interfere with his duties. Outside his role, he practices calligraphy and maintains a deep appreciation for tea, often sharing it with visitors.

Acting as the unofficial leader and tactician among the Guardians, Ōmi coordinates group strategies during conflicts with Logos, the antagonistic organization seeking to unseal Onikirimaru. In the second season, he stages an apparent betrayal by joining Logos, leading to initial condemnation from allies. This action is revealed as a calculated infiltration to retrieve five sacred artifacts belonging to the Tamayori Princess. Undercover, he encounters Vier, a homunculus created by Logos member Drei in the likeness of his deceased mother, intensifying his personal stakes. His disdain for Drei extends beyond Vier to broader ideological clashes.

Throughout the series, Ōmi provides steadfast support to Tamaki, especially during crises involving the seals or emotional turmoil among the Guardians. His development balances his calming presence with the weight of his traumatic history, driving his commitment to prevent further sacrifices while ensuring the Tamayori Princess's safety.