|This article is about a/an spin-off story in Kamen Rider 555.|
Lost World (ロスト・ワールド Rosuto Wārudo) is the Kamen Rider 555 Edition of S.I.C. Hero Saga, based on Kamen Rider 555 published in Monthly Hobby Japan magazine. It serves as a prologue to the alternate story that was Kamen Rider 555: Paradise Lost, and features the new character Riotrooper Ver. 2 (ライオトルーパーver.2 Raiotorūpā ver.2). The story ran from October 2005 to January 2006.
Faiz (ファイズ Faizu)
Takumi Inui and Keitaro Kikuchi are having a stroll when they find a girl, named Mami, crying in a playground. She tells her mother turned into a monster and attacked her. Takumi brings her home but finds that her mother, and all the people in the block, are Orphnochs, with the two escaping from the monsters.
Keitaro gets a phone call from Syuji Mihara, warning him about the blue roses, stating that anyone who touches them will either turn to ash or into Orphnochs. All the other Ryusei High School members had turned to ash except for him and Saya Kimura, who turned into an Orphnoch.
Kaixa (カイザ Kaiza)
A group of Riotroopers appear and start attacking people but are defeated by Kusaka as Kamen Rider Kaixa, who does it on his own.
Delta (デルタ Deruta)
Mihara as Kamen Rider Delta meets up with Kusaka and Mari, and another Riotrooper appears. This Riotrooper, the Riotrooper ver. 2, has a different appearance from the others and is equipped with the Faiz Edge. Kaixa and Delta fight him, damaging his helmet and revealing his identity as the Rose Orphnoch
With Kaixa and Delta being unable to stand up to the Riotrooper v2, they run away with Mari. However, thinking that it was Mihara who sent Mari the roses, Kusaka grabs and tosses him back at Murakami, remarking that he deserves it for daring to send flowers to his beloved woman. Mihara screams that it is a misunderstanding and for Kusaka to help him. Kusaka instead sneers as a blue petal lands on Mihara's outstretched hand, turning him to ash.
Takumi arrives on the scene and runs into Murakami, now in his Rose Orphnoch form, as the Riotrooper V2 was badly damaged.
Psyga (サイガ Saiga)
Murakami utilizes Delta’s Mission Memory to power up his Faiz Edge in order to battle Takumi. Mari then appears and tosses Takumi the Faiz Blaster, causing Murakami to curse her as he was searching the area for it.
Takumi transforms into Kamen Rider Faiz Blaster, and use the Photon Breaker to decapitate Murakami, departing afterward.
Back at their home, Takumi asks Keitaro what happened to Mami, a young girl the two had found and taken in, having left her with him before heading off to look for Mari and Kusaka. Keitaro points to a small human-shaped pile of ash, revealing that she was an Orphonoch as well. Kusaka reveals that he killed the girl himself before she could transform into an Orphnoch much to Takumi's anger.
Meanwhile, Murakami’s head is rolling about when the Lion Orphnoch picks it up. Murakami asks him to bring him back to the Smart Brain headquarters, and to recover the Delta Driver at the same time, utilizing its remains to create the “Emperor’s Belts”. The Lion Orphnoch, seemingly a foreigner, speaking in broken Japanese, replies that he will do so on the condition that he is given one of the belts. Accepting this offer, Murakami promises Leo the Belt of the Sky, the Psyga Driver.
Lost World ends where Paradise Lost started, acting as a prequel for the movie.