Mayonaka no Cinderella* (真夜中のシンデレラ)
Kodansha (講談社): Kodansha Comics Nakayoshi (講談社コミックスなかよし)
Shinsho-ban (新書版)
ISBN-10:4-06-108402-X, 02/1982
Tenshi no Satsui* (天使の殺意)
Kodansha (講談社): Kodansha Comics Nakayoshi (講談社コミックスなかよし)
Shinsho-ban (新書版)
ISBN-10:4-06-108431-3, 02/1983
Other Works
I’ve found mention of other short works by Koiwa such as Peace from Nagasaki (ピース・フロム・ナガサキ) and Peppermint no Kaze no Naka* (ペパーミントの風の中). As far as I know these were never released in book form.