Saki Mitsurugi

"An old friend said, "To know the way to heaven, you must know the way to hell.". We have found a monster that will reach Earth for the first time in 1300 years. That monster's arrival prediction is two months later. On the other hand, we will carry out an annihilation operation with Earth split into fragments as a result. If you have any means to escape, please run away. Those who can not escape ... I'm sorry."

- Saki Mitsurugi in Aizen Tech's announcement news.

Saki Mitsurugi (美剣) is a mysterious girl and the secondary antagonist character replacing Makoto Aizen/Cereza from episode 16 and onward, she is an addition to the cast of Ultraman R/B later on in the series.

Originally credited as the Mysterious Woman (謎の女性) in episodes 11 to 13, she reveals her name during her first meeting with Asahi Minato.

Pre-Ultraman R/B
Saki Mitsurugi (as Grigio Bone) alongside her brothers ; Rosso and Blu was the three warriors sent from Planet O-50, defending Earth from the threat of Reugosite. However, the siblings loss the battle and crashed down towards Earth as a meteor, in what become known as Ayaka City. Saki griefed over the loss of her brothers, who had become scattered as the R／B Crystals. Following this events, Saki travelled around the Earth for centuries and had met several notable figures during her past.

Ultraman R/B
Saki Mitsurugi first shows up after Ultraman Orb Dark defeats Horoboros, and she takes its R/B Crystal. She then appears when Orb Dark and Ultramen Rosso and Blu start to fight, and she summons Horoboros, which somehow evolves into its Bipedal form. After Horoboros defeated the Ultras, Saki called the Kaiju back in its R/B Crystal before summoning again later on to fight Rosso and Blu, who was able to defeat it with the Triple Origium Ray. Afterwards, Saki posed as a nurse and entered Aizen Tech and meeting an injured Makoto Aizen for the first time. Saki also shown her interest towards Asahi, leaving the R/B Crystals of Belial and Ultraman behind after meeting her personally and having a brief conversation with her before lending Makoto her Gyro, stating that she despised weak Ultramen, and allowed him to transform into Grigio King. Makoto successfully took his revenge against Rosso and Blu. Saki then declared herself as the new master of D.R.L.N. while overseeing the battle.

Seeing that the brothers could not use the two new Crystals, she had D.R.L.N. activate the Monster Restraint System, but later rescinded it. Following Grigio King's defeat by Ultraman Ruebe, Saki separated Cereza from Makoto's body and trapped him within the building premises and took over Aizen Tech as its new president, replacing Makoto, who had returned back to normal. However, this was all part of a much bigger plan. Saki continued to interact with Asahi, trying to convince her that she was not really part of the Minato family.

Powers and Weapons

 * Longevity : Saki has lived a very long life, having met Tokugawa Ieyasu during the late sixteenth century, as well as figures such as Oscar Wilde , William Shakespeare , and Niccolò Machiavelli.
 * R/B Gyro -Saki Mitsurugi Specification- : A repainted version of the original Gyro, it sports orange and black accents. It is stated to be the first Gyro created.
 * Kaiju Summoning/Transformation : In the same vein as Makoto Aizen, scanning R/B Crystals allow her to summon or transform into the corresponding Kaiju.
 * Empowerment : A unique feature of her Gyro, Saki can evolve monsters summoned from R/B Crystals into their stronger forms, or at the very least grant them new powers.
 * R/B Crystal Creation : From a monster's remains, Saki can extract their essence and condense it into a R/B Crystal.
 * R/B Crystals : Although she is yet to have her own set, Saki can still use the R/B Crystals on her own Gyro.
 * Kaiju Return : Saki reverts a summoned monster back to its R/B Crystal, which flies back to her.
 * Teleportation : Saki is capable of disappearing within the blink of an eye, doing so to escape before Katsumi witnesses her presence.
 * Energy Pulse : Saki releases a pulse of energy from her hand, which was used to expel Cereza from Makoto Aizen's body.
 * Barrier : Saki puts up an energy barrier to defend herself and others.
 * Healing Wave : Saki is able to heal people, seemigly at the expense of her own energy.

Kaiju

 * Horoboros: Retrieved after the Kaiju's first defeat.
 * Grigio King: Unknown
 * Neronga: Unknown
 * King Joe: Retrieved after the Kaiju's defeat

Ultra

 * Ultraman (Given to Asahi Minato)
 * Ultraman Belial (Given to Asahi Minato)

Other

 * Blank Crystal

Quotes
Whenever Saki expresses her thoughts towards the Ultramen or when talking to others, she will occasionally quote a statement said by one of the historical figures she met in the past. She usually starts with "An old friend once said.....".
 * "Most people are other people, naturally", that goes for those Ultraman, too. "Their thoughts are someone else's opinions, their lives a mimicry, their passions a quotation." (Oscar Wilde)
 * "All the world's a stage, and all the men and women merely players." (William Shakespeare)
 * "To know the way to heaven, you must know the way to Hell." (Niccolò Machiavelli)
 * "There's only one thing worse than injustice, and that's justice without her sword in her hand." (Oscar Wilde)
 * "There is something terribly morbid in the modern sympathy with pain." (Oscar Wilde)
 * "The greatest mistake of the world, is differentiating between good people and bad people." (Oscar Wilde)

Trivia

 * In her intro card during the opening sequence, there are three gray blobs which seem to vaguely resemble the three Grigio variants.
 * The color of her fingernail paint represents the three Ultras:
 * Red: Rosso
 * Blue: Blu
 * Black: Orb Dark, removed after he was defeated by Horoboros.
 * For reasons unknown, she disguises herself when meeting different people, such as a nurse (towards Makoto) and a high school girl (towards Asahi).
 * Her given name is shared with an alien girl from Ultraman Tiga, who also wears black clothes and has been on Earth since the ancient times.
 * It is unknown how Saki could be Rosso and Blu's sister, if she could be Ultrawoman Grigio, or otherwise.