In 1992, his first novel Yume no ki ga tsugeta nara ("If Only the Dream Trees Could Touch") appeared in Hayakawa Shobo (Tokyo)'s SF Magazine. His short story "Spice" won the Hayakawa Award in 1993.

In 1996, he published his first long novel in three volumes, Seikai no Monshou (Seikai no Monsh?/Crest of the Stars). In the next year 1997 Seikai no Monsho was awarded withSeiun Award at the Japan SF Convention. He released its sequel Seikai no Senki (Banner of the Stars), where he said that Seikai no Monsho was actually an overture to Seikai no Senki. Morioka had already suggested in Seikai no Monshou 2 that the entire series should narrate the life of Princess Lamhirh (aka Lafiel), from her birth to her eventual ascension to the imperial throne. Three volumes of Seikai no Senki are now available and Morioka named them "Diahoc Trilogy" but the series itself has not yet finished. An English translation of "Seikai no Monsh?/Crest of the Stars" has been published by Tokyopop, which came out from the fall of 2006 to May of 2007.

Aside from the Seikai series, he published another Senki in 4 volumes, based on Japanese mythology.

His characteristics as a writer include a deep interest for linguistics (specially for conlangs), artificial intelligence, bitter humor, and well-designed world settings.

• If Only the Dream Trees Could Touch (1992)
• Metaldam (1997)
• The War Between Moon and Fire (2000)
• The War Between Moon and Darkness 1-3 (2003)
• Gentle Purgatory (2005)

Seikai Series

Seikai no Monsh?

• Seikai no Monsh? I "Teikoku no ?jo" (Crest of the Stars I "Princess of the Empire") (1996)
• Seikai no Monsh? II "Sasayaka na Tatakai" (Crest of the Stars II "A Modest War") (1996)
• Seikai no Monsh? III "Iky? e no Kikan" (Crest of the Stars III "Return to a Strange World") (1996)

Seikai no Senki

• Seikai no Senki I "Kizuna no Katachi" (Battle Flag of the Stars I "The Form of Bonds") (1996)
• Seikai no Senki II "Mamoru Beki Mono" (Battle Flag of the Stars II "That which is to be Protected") (1998)
• Seikai no Senki III "Kazoku no Shokutaku" (Battle Flag of the Stars III "A Family Dinner") (2001)
• Seikai no Senki IV "Kishimu Jikuu" (Battle Flag of the Stars IV "Cacophonous Space-Time") (2004)

Seikai no Danshou

• Seikai no Danshou I (2005)
• Seikai no Danshou II (2007)