Hiroshi Rara exists as distinct counterparts across parallel worlds. In World A, he is a Nobel Prize-winning scientist and former partner of Ken Sanada. In World B, he steals alien technology, ignites a war, and transforms into the conquering General Rara, leader of the Rara Army. He previously maintained a scientific partnership with that world's Ken Sanada before their conflict. His wife, Ayuko, collaborates in his conquest, and together they have a daughter, Mitsuki Rara.

Despite his role as a conqueror, Hiroshi displays a domestic, caring side within his family, preparing dinner settings, showing interest in Mitsuki's life, and extending warmth to her friend Kazuki during a recovery stay. He justifies conquest as preventing alien technology from falling into "wrong hands," believing himself the most suitable guardian due to his scientific prowess and perceived benevolence. He also enjoys the war's theatrical, game-like structure and his leading role. However, Ayuko usurps his authority, discards the games for ruthless tactics, reduces him to a janitorial role, and even endangers their daughter.

Hiroshi regains agency during a critical attack on their command ship. When Ayuko demands a fight to the end, he slaps her, orders surrender, ensures her evacuation, and prioritizes the safe evacuation of all personnel before the ship's destruction. His scientific expertise proves vital in diagnosing a dimensional crisis; he theorizes that the coexistence of Kazuki and the alien robot Zinv in the same world causes catastrophic dimensional fracturing and collisions. Following Zinv's apparent destruction and the subsequent merger of the two worlds into one stable reality, Hiroshi and Ayuko relocate next door to the Sanada family. His goal is to observe Kazuki and uncover the secret of his connection to Zinv, which reappears unexpectedly. After confirming Zinv's survival, Hiroshi reconciles with Ken Sanada, and they jointly persuade Kazuki to utilize Zinv for space exploration.

Expanded lore connects Hiroshi to a broader universe. After the series' events, he joins Kazuki's space exploration using the alien technology. Their efforts, spanning a billion years prior to another timeline, establish the "Great Prehistoric Civilization," seeding human life and technology across the galaxy. Artifacts from this civilization later become subjects of study and conflict. Hiroshi's astral essence undergoes reincarnation cycles influencing galactic history. Within a specific recent cycle, his astral reincarnates as Ken Raraiba Steinbeck, father of Kiriko Masaki. This reincarnation appears intertwined with the astral essence of his former partner, Ken Sanada, who reincarnates as Hiroshi Manada, creator and father of Miki Steinbeck.