Rosso along with Blu and Grigio were a trio of orphan siblings born on the war-torn Planet Sanja (惑星サンジャ Wakusei Sanja), having been raised along with other orphaned children by Bakubarba (バクバーバ Bakubāba) in a place known as the House of Bakubarba (バクバーバの家 Bakubāba no Ie). The siblings have elite skills in the fields of killing and other illegal activities, which makes them useful tools for Bakubarba, who frequently sends them out on missions. Having no records and no relatives, they were also easily disposable should they fail their job.
The youngest sibling, Grigio, starts to have doubts in killing others and her way of life through each time she only needed to be advised by her brothers and Bakubarba to get back to work. One day, Bakubarba was contacted by Mr. Largo (ラルゴ氏 Rarugo-shi) to kill the monster Nero (ネーロ Nēro), the guardian god of the Bosco Tribe (ボスコ族 Bosuko-zoku) on Forest Planet Dontak (森林惑星ドンタク Shinrin Wakusei Dontaku). Bakubarba sends the trio via spaceship. When the siblings search a dark forest on Planet Dontak, Grigio encounters Bianca (ビアンカ Bianka), a woman who is about to be sacrificed to Nero, but she seems happy, which Grigio cannot understand. The siblings later interrupt the sacrificial ritual to combat Nero, but Grigio tries to convince Bianca to turn against her fate, much to her brothers' dismay as Nero had not yet fully emerged, while angering Nero who tries to kill the siblings. Bianca instead allows Nero to transplant its weak point into herself, so the three siblings have no choice but to kill her along with the monster. The incident left Grigio traumatized. After the siblings leave, the mercenary unit Largo Protege (ラルゴ子飼い Rarugo Kogai) bombs the Boscos with napalms, so that Mr. Largo is able to "modernize" the planet and take the rare minerals there for himself.
Rumors about the three siblings spread and they are constantly under attack by gangs whose members they killed before. Under Bakubarba's advice, they escape to Planet Alhara (惑星アルハラ Wakusei Aruhara), a relatively obscure planet. The people there face frequent water shortages during farming, so the siblings decide to help them by digging up water from underground. The siblings discover a new way of life, which was to give and not to take. For the first time in a long period, Grigio was happy and would like to make this planet her new home. Unfortunately, the reputation of the three siblings means that they would eventually be found and the people of Alhara will suffer because of them, so they have to leave again. They go to Planet Alcatraz (惑星アルカトラズ Wakusei Arukatorazu), which is full of criminals. In a bar, Grigio overhears a rumor about the Warrior's Peak of Planet O-50, and wanted to obtain the power there to become an Ultraman so that she could achieve peace without sacrifice. However, her brothers dismiss her, saying that it's just a fairy tale.
While escaping from the Balsas Gang (バルサス一味 Barusasu Ichimi), they crash land on Planet O-50, near the Warrior's Peak, which Grigio believes is fate. They meet Frau (フラウ Furau) in a hut at the base of the mountain, and she tells them they would need oxygen inhalation devices (酸素吸入装置 Sanso Kyūnyū Sōchi) to climb up the mountain. The Balsas Gang appears and takes Frau hostage, but the three siblings beat them. Unfortunately, they unleash Margodon, who they have no chance of beating. They decide to put the only oxygen inhalation device on Frau, not wanting any third party to get hurt because of them, and climb up the Warrior's Peak, but were stuck in a dilemma whether to attack from there or climb down the other side. Suddenly, the Ring of Light appears to them, giving them the Gyros and R/B Crystals, which they use to transform into Ultraman Rosso, Ultraman Blu and Grigio Bone to defeat Margodon, the Balsas Gang and rescue Frau.
They go on more adventures and gather more R/B Crystals, and eventually become recognized by the Interstellar Alliance. However, Grigio cannot understand why she transforms into a monster. They are sent back to Planet Sanja to inspect on Bakubarba, but discover that the House of Bakubarba has become a child trafficking hub. Bakubarba tries to guilt-trip the siblings, saying that after Mr. Largo acquired Planet Dontak, he sold it off to the Interstellar Alliance, who are also profiting off it. Grigio gets fed up and kills Bakubarba after being taunted. The Balsas gang hears about this and unleashes the monster Fearmonger (フィアモンガ Fiamonga) to kill the siblings. The brothers try to fuse the crystals of light and darkness into a new power, but they fail because they do not connect with Grigio's wishes. Eventually, Rosso, Blu, and Grigio defeat Fearmonger without making any sacrifices.
The siblings are then dispatched to Planet Gion (惑星ギオン Wakusei Gion) to help Zarra Tribe (ザーラ族 Zāra-zoku). Alien Egon Ciel (エゴン星人シーレ Egon Seijin Shīre) created the Murderous Robot Weapons Barrigator 1 and 2 (殺人ロボット兵器バリゲー ター1号・2号 Satsujin Robotto Heiki Barigētā 1-gō 2-gō) to kill everyone there so that he could take the rare metals for himself. The siblings try to convince the people to evacuate, but they do not listen, saying their god will protect them. The boy Verte (ヴェルテ Verute) shows Grigio a book about a legend of a red dragon, who is said to bring destruction. Grigio becomes Grigio Bone to scare everyone away just before Barrigator 1 arrives to fight Ultramen Rosso and Blu. Barrigator 2 suddenly appears before the escaping people, who fight back after seeing Verte step up. Grigio created the Attack crystal from this event through their combined will and became Grigio Regina, who easily defeated Barrigator 2 and Ciel along with it. Grigio is exhausted and turns back into herself, and is taken care of by the Zarra people, who bow to her after she awakens. Rosso and Blu meet up with their sister after defeating Barrigator 1.
The Ring of Light calls the siblings to Urban Planet Nepta (都市惑星ネプタ Toshi Wakusei Neputa) to defeat the rampaging Reugosite, who had its genes tampered with by a certain blue Ultraman. The siblings used their Gyros to turn the gaseous monster into a solid, but their Gyros' output is weak and the monster is stuck in an intermediate form, which destroys the planet. Unable to sit and watch, Blu attacks, ruining the plan. Rosso and Grigio have no choice but to attack as well. Freezing the monster using the Water and Wind crystals, they throw Reugosite into space but it regains its gaseous form. Grigio Regina is knocked back down into King and then to Bone. Due to their intense battle, a wormhole was opened and they were all sucked into it, and they ended up near the planet Earth, which Reugosite sought to drain the life energy out of and then destroy.
"Grigio...you must... live..."
- ―Rosso's and Blu's last words to Grigio
Rosso and Blu defended Grigio by entering a beam lock with Reugosite. However, the siblings lost the battle and crashed down towards Earth as a meteor, in a place that became known as Ayaka City, spreading Ray Energy throughout 1300 points of the Earth as a result of the impact. Grigio grieved over the loss of her brothers, who had died and become scattered as R/B Crystals.
Rosso's powers were transferred to Katsumi Minato, who became Ultraman Rosso in the present day.
Powers and Weapons
- R/B Gyro: Rosso possess this device in order to transform into Ultraman Rosso.
- R/B Crystals: Rosso uses the R/B Crystals in conjunction with the R/B Gyro in order to assume the various elemental forms of Ultraman Rosso.
- Mercenary Skills: Rosso and his siblings are all skilled in combat and weaponry. As noted by Bakubarba, their skills grows rapidly from simple thefts and assassination to monster elimination.
- Crossbow: Used during the theft of rare minerals from the Snark-riding smugglers.
- Anti Monster-Use Heat Ray Gun (対怪獣用熱線銃 Tai Kaijū Yō Nessen Jū): A ray gun used in fighting against giant monsters. Only seen in fighting against Nero.
R/B Crystals in Possession
All Crystals were lost after his death and collected by Katsumi and Isami.
- Ultraman Taro
- Ultraman Ginga
- Ultraman Zero
- Ultraman X
- Ultraman Tiga
- Ultraman Orb
- Spacium Zeperion
- Orb Origin
- Ultraman Victory
- Ultraman Belial
- Given his deliberately very similar appearance to Katsumi, the latter may be Rosso's reincarnation, but this has yet to be confirmed.