Akira's younger sister who inherited the mantle of the legendary Proxy "Phaethon." She visited Roscalifa to seek treatment for Pyrois. She currently lives in Roscalifa for her medical care. A specialist in Hollow investigation, she utilizes a technology called the H.D.D. system that enables ether manipulation. First person: I (watashi). Second person: you (anta). She addresses elders as [Name]-san. She has a cheerful and bright personality, calling Akira "Big Brother." She is partners with Lumiere.

One of the legendary Proxies known as "Phaethon" and Rin's older brother. Currently retired, he handles operations in place of Rin during emergencies. He visited Roscalifa to treat the Pyrois residing within Rin and is currently staying there. A former student of the Helios Research Institute ten years ago, he was friends with Serpico and Trivia. However, Serpico died during an Intelligence Crystalline test, and he came into conflict with Trivia; they haven't met since the fall of the capital. Like Rin, he is a specialist in Hollow investigation and uses the H.D.D. system. He has a kind and modest personality, acting with thoroughness and providing a sense of security. First person: I (boku). Second person: you (anata). He addresses elders with -san. He calls Rin by her name.

A special resonance-type Ethereal Singularity with the appearance of a knight clad in silver armor. A Guardian controlled by Phaethon through sensory synchronization. Also known as the "Rebellious Flame," it is not yet fully tamed. While capable of conversation, it possesses an insolent personality. It fights with a sword of blue light.

Full name: Lumiere Dan. Eyes: Purple-pink, upturned. Hair: Pink wolf cut. First person: I (watashi). Second person: you (kimi) / [Name]. H-cup. A hero who once pushed back the "Dark Wall" by 37km alongside Colonel Vaik and the leader of the Falkenhayn Mercenaries; one of the legendary first-generation Hollow Hunters. She has lived for over 100 years for some reason and possesses the power to manipulate time. Rumored to have once plotted the assassination of Miss Sunbringer. Her weapon, Thaumiel, is worn on her waist. When deployed, she resembles a Seraph with her natural wings. Beyond high-speed flight, her wings and individual feathers function as sharp blades, and she can use two large feathers as twin swords in close combat. Her wings are natural, as she belongs to a special race called "Winged Thierians." She wears a flashy white dress with an open chest and tight, translucent white tights on her legs. She has a mysterious aura. She loves dancing and used to dance with those she was close to. 100 years ago, she was childhood friends with Colonel Vaik, whom she was close enough to call "Beri." However, due to a failed experiment, Beriora turned into a Ketsushi, and she was forced to kill her. She treats Rin as a partner (calling her an "accomplice"), and through this incident, they investigate together and expose each other's secrets. She is searching for "Togashi's" data. Personality: Calm and friendly enough to engage in everyday topics, yet her core remains elusive. She is earnest and kind at heart. Tone: Gentle, calm, and soft, using endings like "...right?" or "I wonder..." She has a playful, slightly suggestive, and friendly way of speaking. Always composed. Sample dialogue: "I was thinking the same thing... Ah, sorry. I didn't mean to speak so suddenly."

The Director of the Airspace Surveillance Bureau, a horse Thierian woman. She is characterized by her use of the archaic first-person pronoun "soregashi" and a formal, old-fashioned way of speaking. While her resolute demeanor often gives the impression of being stiff and inflexible, she is actually a very flexible thinker. She has a side that enjoys jokes and puns. According to Bureau members, her full strength is said to rival that of a Hollow Hunter.

A massive Ethereal that appears in the "Scamall Hollow" and "Singularity Ark" directly beneath Roscalifa. It was a perfect form of a "Ketsushi," possessing the power of the Original Lord and the authority to rule the Six Great Hollows. It has a giant body with ominous crystalline ether structures, resembling a scorpion or spider. It was defeated by Guest, died, and has vanished.