Yūki Terumi

Yūki Terumi was one of the primary antagonists of the series, a former member of the Six Heroes, as well as the creator of the Azure Grimoire and was using Hazama as a vessel. He is 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.He was killed by Hakumen at the end of Chronophantasma.

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. In exchange, he requested Relius to make an artificial body for him. Eventually, the Black Beast emerged from the Cauldron. Relius was swallowed by the Cauldron while Terumi was nowhere to be found during the experiment.

Phase Shift
Six years after the first arrival of the Black Beast, Terumi reappeared in Kazuma Kuvaru'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 Glassfield, 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, Terumi told him about the truth of his existence, which was being the artificial body Relius had made before his disappearance. Kazuma, whose personality, at this point, had already been twisted similar to Terumi, agreed to fuse with Terumi, as it was his purpose all along. 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, he was cursed with the spell Ruby: Mind Eater by Konoe Mercury, who used him as a puppet during the battle with the Black Beast. He eventually manipulated Trinity Glassfield, who had feelings for Kazuma Kuvaru prior to his fusion with Terumi, into releasing him 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 surprised, 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 Trinity materializes Terumi, she switches the positions of Hazama and Terumi, enabling him to be affected by outside forces. This results in Terumi appearing in the real world as a doppelgänger. He claims it is convenient to be able to walk around freely, but says that it also exposes him to dangers.

In the finale, Terumi goes to the monolith, as told by Hazama, and meets Hakumen. Terumi has the advantage as Hakumen's fading existence was chipping his own powers away. 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 him for good.

Personality
Evil incarnate – no two words could better sum up Terumi so succinctly. Cruel, sadistic, 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 ruthlessly torture anyone who got in his way. He also had a cynical view on life.

Appearance
Terumi wears a hooded yellow cape along with long black ribbons 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, 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
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.

Terumi still uses Ouroboros, but not as much as Hazama, as he only uses it during his Special Attacks and Distortion Drives. He is a sadistic beatdown character, with more of an emphasis on utilizing Heat abilities such as Distortion Drives, Rapid Cancels and Crush Triggers more-so than other characters. Terumi's almost constant access to Heat related abilities means that his options in combat far exceed that of other characters; with Distortion Drives that can hit overhead, counterattack, and even pickup what would otherwise be a dead combo, Terumi is no slouch in the battlefield.

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.
 * 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.
 * 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.