In my au, Iwao (a student of the 80s regime) is the father of Midori (a former insect pillar) and the best friend of the previous plant pillar Hozumi (a student of the 80s), as well as the guardian for Uekiya (the current plant pillar). He himself has a weak respiration of plants.
He saved the girls from the tyrant's father, but later he could not help Teiko and she died at the hands of her demon-turned husband. Small Uekiya after the incident decided to become slayer