Yūki Terumi

Yūki Terumi was one of the primary antagonists of the series and a former member of the Six Heroes, as well as the creator of the Azure Grimoire. He was also the founder of both Novus Orbis Librarium and Sector Seven, often manipulating both sides to reach his goals. He is featured as a playable DLC character in the console version of BlazBlue: Chronophantasma, later being introduced to the arcade version.

Phase 0
When Relius Clover and Shūichirō Ayatsuki worked on an experiment to examine the Gate, Terumi offered his knowledge, as well as the Susano'o Unit, for their studies. During Relius' trial experiment, the Black Beast emerged from the Cauldron. Relius was swallowed by the Cauldron, Terumi's physical form was destroyed, and his spirit form took heavy damage. During the five years it took his spirit form to heal, he followed Relius' last instructions and set out to find Kazuma Kuvaru, the new body Relius made for him before disappearing.

Phase Shift
Six years after the first arrival of the Black Beast, Terumi managed to find Kazuma, though the latter did not recognize him. He appeared in Kazuma's room, offering a way to change his life in exchange for the Azure. At first, Kazuma refrained due to Terumi's unusual aura; however, he was later attacked by three Kaka assassins, and Terumi used the chance to force him into agreement before defeating the assassins with ease. Terumi led Kazuma into infiltrating the Cathedral on the island afterwards.

Kazuma was constantly hindered by Trinity Glassfille, Nine and Celica A. Mercury in his search. Terumi helped him by telling him about the rip in the barrier of the Magic Guild made by the Kaka assassins. This resulted in Kazuma tricking Celica into leaving the island, causing seithr to spread inside the barrier, which would require the Ten Saints's attention and give him the chance to infiltrate.

As Kazuma succeeded, he encountered the imitation Cauldron inside the building and was filled with all information about Terumi. Realizing his true purpose and identity, Kazuma, whose personality, at this point, had already been twisted similar to Terumi, fused with him. After his revival, he was attacked by Tomonori. Terumi emerged victorious, winning the fight with his signature Nox Nyctores, Geminus Anguium: Ouroboros, and killing Tomonori in the process. However, he was captured by Jubei and Valkenhayn and sealed by Clavis Alucard.

Soon after, Konoe Mercury, who realized that Terumi's power was needed to defeat the Black Beast, cast Ruby: Mind Eater on him to use him as a puppet during the Dark War. Before the spell hit, he split his and Kazuma's mind from each other so that his controlled mind was trapped inside his body while Kazuma took over. After the war, Kazuma eventually manipulated Trinity Glassfille, who had feelings for him, into releasing Terumi from the spell.

After his release, he quickly killed Konoe and Trinity, threw their bodies into the Boundary, and proceeded to find Hakumen and Jubei so he could kill them. Terumi had the upper hand, but Jubei used Tomonori's Sekigan to force him materialize. As he was taken by surprise, Hakumen grabbed him and jumped into the Cauldron while Jubei closed the gate.

Terumi was sealed inside the Boundary for some time before being finally released by Takamagahara. He met Relius, who had just finished his time leap after being swallowed by the Cauldron, again and the two resumed their partnership. Relius apparently made Terumi a new body afterwards.

Chronophantasma
As part of their plan, Trinity and Rachel utilize Arma Reboare: Muchōrin on a more powerful level to materialize Terumi in the real world. To do so, they assault Terumi's mind and agitate him by having various illusions of characters he finds particularly annoying to taunt him, such as Bang, Ragna, and his fellow Heroes. Prior to Amaterasu's forced intervention, he even has to fight himself, who claims that even Trinity might have not predict this far. Eventually, Terumi's consciousness is forced to become the front side while Hazama's becomes the backside. The Heroes catch him downtown Yabiko, and almost kill him if not for Phantom's intervention. Terumi somehow manages to become the backside later, and meets Trinity again as the Heroes split up to look for him. He easily defeats Trinity, but Hakumen appears to save her. Terumi traps both of them in Phantom's Infinite Corridor to lock them away forever, but Trinity and Hakumen use the power of Amaterasu and Muchōrin to confront the source of the barrier.

In the finale, he goes to the Monolith as told by Hazama and meets Hakumen. As Hakumen tries to ascertain his existence, Terumi blames what happened on Trinity and Rachel, saying his recognition is all over the place despite finally set free. He then encounters Hakumen in battle. Terumi gains the upper hand by not allowing Hakumen any opening to charge his technique. However, as Trinity ambushes Hazama, the connection between him and Terumi puts the latter into a temporary halt. Using the chance, Hakumen uses Time Killer on Terumi and kills all of his "time", effectively destroying him.

Personality
Cruel, sadistic, selfish, and insane beyond measure, Terumi delighted in the suffering of others, both physically and mentally, and relished pure chaos. He would provoke and manipulate others for his own amusement, and would ruthlessly torture anyone who irritated him or got in his way. Unsurprisingly, this has earned him the contempt of almost every character in the BlazBlue universe, most notably Ragna, Kokonoe, and Nine. However, he is prone to breakdowns when things don't go his way.

Appearance
Terumi wears a hooded yellow cape with black markings and large rolled-up cuffs along with long black ribbons and bandages across his arms. He also retains a few articles of clothing from Hazama's form, including an open shirt beneath his vest that shows his chest, a loose black tie, two belts, and black pants. When he activates Overdrive mode, his hood comes off for a brief moment, revealing his spiky green hair.

Powers and Abilities
Stated by Jubei to be a powerful magic-user, Terumi has shown to be one of the most powerful characters in the Blazblue series. Terumi's primary ability is to feed on the hatred of others to make himself stronger, and it also allows him to anchor himself into the physical world. In ghost form, Terumi is intangible and immune to most attacks save those that are specially designed to harm ghosts, such as Tomonori's Hihīrokane. Despite his incorporeal state, Terumi is still able to physically interact with the world. Terumi was shown to be able to erase memories by "eating" them, commenting that they are delicious. He used this ability twice, both of which were on Jin Kisaragi.

In battle, Terumi is a powerful, vicious, and savage opponent, able to fight on par with both Hakumen and Jubei. In line with his sadism, Terumi's fighting style revolves around inflicting as much pain on his enemy as possible before finally killing them. In contrast to Hazama, who relies on his Ouroboros chains and whose fighting style was graceful and dance-like, Terumi's style is far more barbaric and cruel, relying more on his serpentine spirits and his butterfly knives. He is also adept in the use of his Ouroboros for direct attacks, using it for his Snake Bite, Retaliating Fang, Venomous Bite, and Screeches of the Condemned attacks, being these the only times he uses it as such. Terumi is also able to access the power of the Susano'o Unit despite no longer owning it, using it to transform into the Dark Susano'o, a black and green shadow version of Hakumen, and deal the final blow in his Astral Heat, Unholy Wrath of the Basilisk.

Gameplay-wise, Terumi is a character with more Distortion Drives than special moves. His Drive, Force Eater, allows Terumi to have a much greater Heat Gauge gain while negating it to his opponents, allowing him to utilize his Heat-related abilities far more than any other character and having several combo opportunities to use them, making his potential damage output outright devastating. His Overdrive is Nightmare Reaper, which strengthens Terumi's Drive attacks and allows him to absorb the opponent's Heat Gauge, similar to Ragna the Bloodedge's Soul Eater.

Etymology
The "yū" in "Yūki" is from Japanese 優 yū – "gentleness, superiority" or 悠 yū – "distant, leisurely" is a literal translation. Whereas 希 ki – "hope", 輝 ki – "radiance" or 生 ki – "life" serves as the other half of the translation. However, the most likely translation is 幽鬼 yūki – "ghost" or "revenant".

His last name translates from Japanese as "beautiful shrine" and is a feminine name, although admittedly rare.

Trivia

 * Terumi's crest resembles a caduceus, or "herald's staff", which consists of two snakes coiling around a winged staff. In Greek mythology, it was carried by Hermes, a cunning trickster god who could freely move between the boundaries of worlds as an emissary of the gods and conductor of souls into the afterlife.
 * Terumi is the first character to physically interact with the losing character after a match, stomping on them and occasionally kicking them off the screen.
 * Due to a glitch, Terumi's actions mentioned above count as a combo in Score Attack, with his repeated stomping on Ragna giving him the most points.
 * Just like Hazama, when Terumi is electrocuted, an imprint of his ghost form is revealed instead of a skeleton.
 * It is implied that Terumi's ghost form can materialize at will, but stills need a vessel to anchor his existence in the living world.
 * Terumi has more Distortion Drives than any other character, with a total of 6.
 * Terumi's Astral Heat has exactly the same button and joystick inputs as Amane Nishiki's, Lambda-11's, Mu-12's, and Nu-13's.
 * According to Toshimichi Mori on BlazBlue Radio A episode 5, Yūki Terumi is not his real name.