Gremmy Thoumeaux/Expanded Universe

is a Quincy and a member of the Wandenreich's Sternritter with the designation "V" - "The Visionary".

Beginning of the Revive of Tomorrow
At some point before the first Wandenreich invasion of Soul Society, Gremmy had used The Visionary to create Shaz Domino. While Shaz was originally just an imaginary being like Guenael Lee, his power, The Viability, allowed Shaz to replace every part of his imaginary body with real parts formed from Reishi, and so was able to escape from Gremmy's control. With Gremmy having left Shaz's fate up to him due to lack of interest, Yhwach granted Shaz the Greek letter Sigma and welcomed him as a Sternritter.

Bleach: Can't Fear Your Own World
As Gremmy was released from his secure cage deep inside the Silbern to fight the Shinigami he is approached by the one person he noted does not show fear or apprehension for him, the Sternritter Liltotto Lamperd. As Liltotto exchanged playful banter with Gremmy, she noted her hunger, to which Gremmy used The Visionary to create several pastries and sweets for her.

As Liltotto enjoyed her gift, she invited Gremmy to indulge in some himself, after he has defeated the Shinigami by himself. While Liltotto thanked him for "saving her life", saying she genuinely wants to repay him somehow, Gremmy just asked her to leave as he believes the Sternritter are all selfish, including Yhwach. Liltotto agreed that what Yhwach does to Gremmy is cruel and hoped that after the war ends he can be free. When Gremmy reveals he has no idea what to do with his freedom should he ever get it, Liltotto suggested he learns to cook so he can taste a wider variety of foods.

Eventually the two Sternritter parted ways amicably, Liltotto leaving with Bambietta Basterbine and Gremmy with his newly-created Guenael Lee.

Bleach: Can't Fear Your Own World
Following his death in combat against Kenpachi, Gremmy's inert brain was secretly confiscated by Tokinada Tsunayashiro, who proceeded to use the powerful brain as a core component to create the artificial hybrid Hikone Ubuginu.

During Hikone's battle against Kenpachi Zaraki, it's noted by Candice Catnipp that their personality while fighting Kenpachi began resembling Gremmy's during his final battle against Kenpachi.

Powers and Abilities

 * Gremmy has the ability to turn fantasy into reality. Both Liltotto Lamperd and Gremmy himself implied that Gremmy's long imprisonment at the hands of Yhwach have stunted his imagination, preventing The Visionary from reaching its full potential.

Immeasurable Spiritual Power: Gremmy is noted to have truly colossal amounts of Reiryoku, and is believed by his fellow Sternritter to be the strongest amongst them all. Liltotto Lamperd even expressed a genuine belief that Gremmy is able to defeat the entirety of the Gotei 13 by himself; albeit after Genryūsai Shigekuni Yamamoto was already killed. As a true testament to Gremmy's power, it required Yhwach himself to create bindings that could hold Gremmy captive. Gremmy's raw power is of such a degree that it could force Hikone Ubuginu's outright paradoxical nature to exist anyway.

Trivia

 * Although never outright confirmed, it is repeatedly implied to varying degrees in Bleach: Can't Fear Your Own World that Gremmy may have been an aspect of the Soul King, like Gerard Valkyrie or Pernida Parnkgjas.