In the beginning and middle of the series, the writing and production staff only had the first three volumes of the manga as source. In order to fill the entire 26-episode run of the anime, new characters, new settings and new relationships between characters were made in order to increase dramatic tension, reinforce themes introduced in the manga, and introduce new themes that were compatible with the manga.
The initial three volumes of the manga provided the core storyline for the first part of the series. To create a complete adaptation for the 26-episode anime, additional characters, settings, and relationships were introduced to enhance the dramatic tension, reinforce themes from the manga, and introduce new thematic elements that complemented the existing narrative.