The player follows the story of the titular Opoona as he attempts to find the location of his family from which he was separated after the occurrence of a mysterious accident during their travels.

Species died and vegetation withered in the heat; mysterious creatures, known as Rogues, emerged from the meteorite and began to attack people.

Several hundred years after the meteorite impact, Opoona and his siblings, Copoona and Poleena, are on a family vacation from the star Tizia with their parents, Momeena, Dadeena and co-pilots Troc and Noix, travelling in a spaceship to Landroll.

Opoona graduates from Starhouse as a Level One Ranger, receiving assignments in Lifeborn, Artiela and the Intelligent Sea, where he is temporarily employed by both the Bravo and Shine companies to remove bugs from programming and to also help patients in the hospital ward.

Artepiazza was asked by publisher Koei "to create fun and unique visuals that convey the enjoyment of an RPG in a simple fashion" in place of using state-of-the-art CG and hardware technology available at the time of the game's production.

[4] Rather than utilize the traditional "single hero" or "chosen one" motif of RPGS, the staff members at Artepiazza emphasized the importance of relationships and family in Opoona, with Sachiko Sugimura explaining that every single person means something and that the world grows and changes in accordance with the loving relationships among all people, instead of depicting the main character only as a special existence.

[4][5][6] Art director Shintaro Majima stated that he was first inspired to create Opoona after waking from a nap, taking a bath, and drawing his first design on the bathroom mirror.

[4][5] The main characters were meant to be simple enough that they could be easily redrawn by children; enemies were designed as non-living objects to make them distinct.

Majima's brother Tatuso, a modern artist, planned the locations and landscapes using what he considered to be the most attractive blend of reality and imagination.

[7] Sakimoto arranged the score in an orthodox manner with "futuristic" sounds as he had done with many of his past compositions by combining orchestral music with a synthesizer, but his work on Opoona involved composing the songs through the characters' perspective to somehow lend the player their sympathy.

[10] The project had no publisher until Dragon Quest designer Yuji Horii sparked talks between ArtePiazza and Koei following the Electronic Entertainment Expo in 2006.

[4] Opoona was announced as an untitled RPG in a September 2006 issue of Japanese magazine Famitsu and was unveiled with its finalized title at a Koei press event the following March.

The game was released on the same day as Nintendo's Super Mario Galaxy, a title that Artepiazza and Koei did not foresee as competition being in a different genre.