(These are half headcanons, half canon.)

Age: 39 years

Birthday: January 1

Gender: Trans man, probably nonbinary but he doesn't care

Height: 6'0 / 183cm

Personality traits: Creative / Conniving / Faulted / Overly dependent on those he cares for most / Well intentioned / Thrives in crowds

Hobbies: Placing together blank jigsaw puzzles / Listening to music

Specialties: Command of language / Perfect pitch / Cursive handwriting

Likes: Nothing in particular, when in a dissociative state / The beauty of humanity / Family in all of its ways

Dislikes: Silence / Confined spaces / Empty rooms / The unnerving cleanliness of science equipment

Mental health: Autistic / Borderline with psychotic traits / Undefined dissociative

Animal motif: Sheep

Argalia, also known as the Blue Reverberation, the Conductor of the Ensemble, and a "certified lunatic", is quite the interesting character! The main villain of Project Moon's Library of Ruina, he appears often in the game, first introduced in person with the Full-Stop Office while the Library is labeled as an Urban Plague. Before the events of the game, he had a traumatic past in which he and his sister Angelica were experimented on as children. This led to him becoming incredibly attached to Angelica, attached to such a degree that his abandonment issues latched onto her. Eventually, he became a Color Fixer, the highest rank of Fixer in the City, alongside his sister. He was the Blue Reverberation while Angelica was the Black Silence, a title eventually passed onto Roland.

When Angelica began to date Roland, he felt as though Roland was intruding on his life. Angelica was all he had, after all. There was always animosity between the two, but after Angelica died, he fell into a dissociative state influenced by Carmen, the voice of the Distortion. He gathered Distortions one by one, despite not being a Distortion himself, believing them to be the true form of humanity. He felt no purpose in life and liked nothing in particular, and saw using the Library's Light to turn the City into Distortions as his way of making an impact; of finally feeling human after a life of being alienated. The Ensemble brought him camaraderie that filled his soul even when he thought he had nothing left after Angelica.

Only for them to also perish one by one in front of him, turning into books before he did as well. However, once the Light was unleashed, he came back with them, now a Distortion. It doesn't take long for him to meet his final end at Roland's blade, who says he should've acted like a lunatic to the very end.

My view of Argalia in LOR is that he's... unhinged, to say the least, but with good intentions. He wants his life to mean something, and he's always felt hollow inside. The day Angelica died to the Pianist was the best and worst day of his life. Sure, he lost his sister, but in his eyes, she became part of something much greater than herself. She became a part of a song, and not just any song, but the song that he hoped would bring a new City. Though he's a villain that at first glance can seem stereotypically insane, he actually has much more depth and a backstory that forms his worldview. I feel almost as though Carmen became a replacement for Angelica in his mind as someone to be dependent on. Perhaps her voice and tone was almost sisterly to him, and Carmen took advantage of that. He truly believes in her vision to save the City from the "disease of the heart", and that everyone becoming a Distortion would make his life mean something and turn him into a hero. A hero, something that he always saw Angelica as.

Argalia is based on the character of the same name originally from the epic poem Orlando Innamorato by Matteo Maria Boiardo. Library of Ruina takes heavy inspiration from what's pretty much 1500s-era fanfiction of it by Ludovico Ariosto (lol), Orlando Furioso. I still desperately need to read both stories, so please note that everything else I'm about to say comes from plot summaries. In Innamorato, Angelica and Argalia are the children of the king of Cathay. Angelica offers herself as a prize to whoever can defeat Argalia in battle, who takes on the role of a knight named Uberto dal Leone. He dies shortly after, unfortunately.

On that note, Uberto was his pseudonym in the laboratory. The name means "to enrich", yet Argalia found it uninspired.

The blue thing on Argalia's head is a device that plugs into his ear. It primarily plays white noise alongside the sound of crowds and people talking.

Argalia's voice actor is Hwang Chang-yung, who also voices Jia Huan in Limbus Company.

His scythe reverberates at high frequencies, leaving a vibrating echo wherever he goes.

Meaning "hope", his birth flower is the snowdrop. This was considered by the developers!