"Why did you disturb us!"
- ―Renki's quote when awakened
Subtitle: Vengeful Demon (怨霊鬼 Onryō Oni)
Sometime ago a civil war raged within Japan. Two lovers, a soldier general and a princess, from different sides fell in love with each other but they knowing that the war would keep them apart they commited suicide. But their spirits could not find peace and together they formed the ghostly samurai, Renki and terrorized Japan, but a samurai named Kagetatsu Nishikida appeared and seal the restless spirits beneath the ground sealed by a magic stone.
As time passed and now in the modern era, two developers destroyed the seal in order to create a dam, freeing Renki to terrorize Japan in the modern era. With attacks from Team EYES and Ultraman Cosmos proven ineffective, Shinobu appears, telling the samurai that falling in love would not be easy as expected and a lot of obstacles had been went through for lovers to achieve their happiness. Touched by her words, Renki disappeared with the two deceased lovers' spirits finally rest in peace.
- Suit Actor: Tadashi Katsumata
- Voice Actors: Miho Aoyama, Tadashi Katsumata
- The fate of the two lovers who committed suicide to be together, is similar to the ending of the play Romeo and Juliet written by William Shakespeare.
- He is similar to Sakunaoni, since they are ghosts/yokai with advanced swordsmanship and both were defeated by the same enemy.
- Renki is the second monster after Hoe to be made up from a combination of the feelings of love and vengeance.
- The samurai armor worn by Renki was never a part of the suit, as director Muraishi borrowed it from a certain period drama.
Renki reappeared in this series in episode 19 as Gurenki (
In the Pacific records, Renki was a mentioned as vengeful spirit born from a couple composed of a commander and a princess torn apart by conflicts that was common in the Sengoku period. Driven by envy towards those blessed with romantic fortune, the spirit manifests as a blood red armor-clad samurai who terrorized brides during their wedding. The samurai spirit was finally put to rest by a monk who sealed it into a stone, and ever since then, Renki was able to use his powers to grant human wishes while being contained inside the stone.
In the present, Naomi Yumeno tried to wish on the stone after a unfortunate time at her friends bachelorette party, but Naomi took it back and threw her broken high heels at it. However, Renki didn't respond to that very well. Renki first appeared as a spirit and traveled to the Wishing Stone via shadow portal after glancing at Naomi and her friends.
Renki reappeared the next day in his gigantic form wearing Naomi's shoes and heading towards the hotel. Gai then transformed into Ultraman Orb Hurricane Slash and immediately summoned his Orb Slugger Lance to challenge to him to a duel. Orb went for using his Trident Slash on the samurai but he dodged it with his enhanced reflexes and then caught the lance himself and threw it away after he kicked and knee striked him.
Renki then brought out his katana when Orb transformed into his Orb Origin form. Even though Renki's skills with a sword proved to be superior to the Ultra's, the samurai put up an evenly matched fight in both close combat and sword fighting. Renki then used his special technique, the Mystic Energy Crimson Lotus Reversal on the Ultra, making him fall and his Color Timer flash.
With the Ultra seemingly taken care of, Renki headed towards the hotel and proceeding to slash it, only to be stopped by Naomi, who reminded him that he used his powers to help those in need and were very grateful for it and eventually, he came to his senses. When he saw Orb again, Renki planted his sword to the ground and let Orb finish him off with his Orb Water Calibur, reverting him back into a spirit and then spread out throughout the sky as a rainbow appeared in it.
- Suit actor: Daisuke Terai.
- His suit is modified from Mechazam/Ghost Rebirth from Ultraman Mebius Gaiden: Ghost Rebirth.
- His attack is a possible reference to Sasaki Kojiro's Swallow Reversal.
- Gurenki's name is derived from the Japanese word Guren, an artistic term used to describe something being as beautiful as a crimson-colored lotus flower.
- A version of Renki was intended to appear in Ultraman X, though this was scrapped. Coincidentally, he would have appeared in episode 19 as he did in Orb.
- Height: 49 m
- Weight: 48,000 t
- Origin: Northwest region, Kono Village
- Powers and Weapons
- Intangibility: Being a ghost, Renki is capable of phasing through attacks even for Cosmos' Full Moon Rect.
- Onryō Sword (怨霊剣 Onryō Ken): Based on one of the lover's past as a general/samurai, Renki is armed with a katana.
- Height: 51 m
- Weight: 51,000 t
- Origin: Unknown
- Powers and Weapons
- Shadow Portal: Renki is capable of moving to a distant location by simply creating a black portal.
- Enhanced Reflexes: Renki is capable of moving at high speeds, using it to counter Orb Hurricane Slash's Trident Slash, which is his fastest attack and catch the Orb Slugger Lance.
- Samurai Armor: In contrast to its original incarnation, Renki wears a set of red Japanese armor, fitted with sode shoulder armor, Kabuto helmet and a Menpō covering the lower part of its Noh mask on its face.
- Katana: Similar to the original Renki is also armed with a Katana and is capable of clashing with the likes of the Orbcalibur, Ultraman Orb's strongest weapon.
- Enhanced Swordsmanship: As one of the components of Renki is the spirit of a samurai, he inherited the former's swordsmanship ability and is able to outmatch Orb, whose swordplay level is intermediate.
- Mystic Energy Crimson Reversal (妖気紅蓮返し Yōki Guren-Gaeshi): Renki charges his Katana with dark energy from his mouth before slicing the opponent with it.
- Energy Slash: In Ultraman Fusion Fight!, Renki can release a red energy slash from his katana.