In the real world, Takuma Sakamoto appears as an ordinary Japanese adult male. He has an unremarkable and somewhat disheveled look, typically seen wearing a collar-stretched T-shirt and frayed half-pants, reflecting his reclusive and laid-back lifestyle as a gamer.

In the fantasy world, Takuma assumes the physical form of his Cross Reverie avatar, Diablo. His appearance is striking and intimidating, he has white hair, sharp black eyes, and distinctive bluish-black birthmarks resembling tattoos that run from his forehead down to his cheeks. A pair of large, curved horns protrude from his head, giving him a devil-like visage, a visual effect granted by the equipment known as The Distorted Crown.

Diablo’s physique is tall, muscular, and dark-skinned, exuding both elegance and raw power. His attire consists of pitch-black armor called The Hollow of Jet Black, complemented by a regal mantle named The Curtain of Dark Clouds, which drapes across his back, signifying his status. At his waist hangs an item pouch, and he wears The Demon King’s Ring on the middle finger of his left hand, an artifact that plays a key role in reflecting the enslavement spell upon his summoning. His primary weapon is the Staff of Tenma, a formidable magical staff that underscores his overwhelming magical prowess.

In reality, Takuma Sakamoto is a deeply introverted and socially awkward individual, particularly uncomfortable around women. His reclusive lifestyle and lack of interpersonal experience make it difficult for him to communicate effectively in real-world social situations. In his gaming life, he often used his character Diablo as a means of escapism, projecting dominance and control to compensate for his insecurities. Notably, he would sometimes vent his frustrations by targeting in-game couples and defeating them, finding a sense of catharsis in his unmatched power.

Upon being transported into the fantasy world in the form of Diablo, Takuma adopts the role of a powerful and aloof Demon Lord, maintaining a haughty and commanding demeanor. This exaggerated persona serves as a mask to navigate interactions he would otherwise find overwhelming. While he convincingly plays the part of the fearsome Diablo, his true personality occasionally slips through especially during moments of emotional vulnerability or social discomfort. These moments often result in humorous or awkward situations, particularly when dealing with the affections or closeness of his female companions.

Despite his awkwardness, Takuma is genuinely kind-hearted and loyal to his allies. His experiences in the new world gradually help him grow more confident, though he continues to rely on the Diablo persona to maintain control and composure.

Before being transported to another world, Takuma Sakamoto lived as a reclusive and socially withdrawn individual. Struggling with interpersonal communication and preferring solitude, he spent most of his time immersed in online games. His main focus was the MMORPG Cross Reverie, where he played as the overwhelmingly powerful character Diablo, known in-game as the “True Demon King.” Through Diablo, Takuma was able to express a confident and dominant persona that contrasted sharply with his real-life timid nature.

In addition to Cross Reverie, Takuma occasionally played other titles, including the anime-styled game Sister Carnival (SisKani) and a modern warfare-themed first-person shooter (FPS), though these were more casual pursuits compared to his commitment to Cross Reverie.

His extensive time spent gaming and mastering the mechanics of Cross Reverie would become invaluable when he was suddenly transported to a fantasy world that closely resembled the game, reincarnated in the body of his character, Diablo.

Volume 1
Takuma Sakamoto awakens one day to find himself in an unfamiliar setting, confronted by two unfamiliar girls—an Elf and a Pantherian. Both lean in to kiss him as part of what they call an Enslavement Ritual. As he regains awareness, Takuma notices that he is no longer in his room, nor is he in his usual clothes; instead, he is clad in the attire of his Cross Reverie character, Diablo. Looking around, he realizes that he is on the summit of Starfall Tower, a well-known location in the game where Summoner-class players summon beasts. He is on the very altar where summoned creatures typically appear.

The Elf and Pantherian begin to argue over who successfully summoned him. The Elf claims she is now a Summoner, while the Pantherian insists it was her summoning. As Takuma processes the situation, he comes to the shocking realization that he has not only been summoned to another world but he has been brought into it as Diablo, his powerful in-game persona.

Internally, Takuma reflects on the mechanics of Summoners and Summons within Cross Reverie, growing concerned over the possibility of being magically dominated or enslaved. Initially flustered by the idea of being dominated by either of the attractive girls, he quickly brushes the thought aside.

The Pantherian girl soon approaches and asks whether he can understand them, to which he verbally responds. His ability to speak surprises both girls, as summoned creatures are generally non-verbal. Their argument over who summoned Diablo resumes, each determined to claim ownership of the powerful entity now standing before them. However, due to the magic reflection effect of The Demon King’s Ring, the intended enslavement spell is reversed enslaving the two girls to Takuma instead.

Rem Galleu
Rem is one of the two girls who summoned Diablo to the other world. A Pantherian with a stoic demeanor, she initially intended to enslave him as part of a summoning ritual. However, due to Diablo’s magic reflection ability, she became bound to him instead. Over time, Rem and Diablo develop a close relationship that gradually becomes romantic. Their bond deepens throughout the series, culminating in their marriage in Volume 9.

Shera L. Greenwood
Shera is the second girl who participated in the summoning ritual that brought Diablo into the fantasy world. An Elf and the princess of the Kingdom of Greenwood, Shera is cheerful, affectionate, and openly expresses her love for Diablo. She too becomes magically bound to him, and their relationship grows over the course of the series. She marries Diablo in Volume 7, marking a major development in their relationship.

Horn
Horn is a Grasswalker, a race known for their agility and small stature. Diablo meets Horn in Zircon Tower City, and the two work together on various quests. Horn often acts as a comic relief character but proves to be a loyal and resourceful ally.

Rose
Rose is a Magimatic Maid, an advanced NPC created by Diablo within his dungeon in Cross Reverie. She resides on the lowest floor of his dungeon and serves him with unwavering devotion. After being reunited in the other world, Rose continues to see Diablo as her master and protector, following him loyally.

Rafflesia S. Orangewood
A noblewoman Diablo rescues from execution, Rafflesia becomes deeply grateful to him. Her gratitude quickly takes a romantic turn, and she attempts to seduce Diablo. The situation escalates, nearly resulting in intimacy, but Rem interrupts before it goes further.

Solami Galleu
Solami is Rem’s aunt and a former adventurer. She takes a personal interest in Diablo and assists in training him, providing close physical guidance. Their interactions are often charged with comedic tension, and she plays a role in Diablo’s growth both as a fighter and a man.