The omnibus format is a popular means for animation studios to dismantle harem anime such that the protagonist is able to court multiple romantic candidates without conflicts and without having multiple partners at one instance.
Omnibus Format Airing Approaches
Amagami SS
Amagami SS was the first anime for which the term "omnibus format" was coined. As such, the airing scheme for Amagami SS was the omnibus format in its purest form: each heroine had a 4-episode arc during which their romantic encounter was completed. By each encounter's conclusion the universe would reset for the next heroine's romantic encounter to begin. All memories of moments that occurred during the 4-episode arc are also wiped.
Essentially, this created short, self-contained stories:
- Episodes 1-4: Haruka Morishima Arc
- Episodes 5-8: Kaoru Tanamachi Arc
- Episodes 9-12: Sae Nakata Arc
- Episodes 13-16: Ai Nanasaki Arc
- Episodes 17-20: Rihoko Sakurai Arc
- Episodes 21-24: Tsukasa Ayatsuji Arc
- Episode 25*: Risa Kamizaki Arc
*Risa is the only heroine to have one episode since her route was actually a secret unlock in the dating simulation game the anime was based on.
Yosuga no Sora
Yosuga no Sora was also aired in an omnibus format, except the approach was drastically different.
Instead of strictly keeping one episode set for one heroine, there were instances in the airing when multiple heroines' universes shared the experiences of one episode. With this, the animation studio was able to fit the stories of its four heroines in twelve episodes such that each heroine's story actually encompassed at least four episodes. (The main heroine, Sora, had her arc actually encompass five.)
- Episodes 1-4: Akira Amatsume Arc
- Episodes 1-2, 5-6: Kazuha Migiwa Arc
- Episodes 1, 7-9: Nao Yorihime Arc
- Episodes 1, 7,10-12: Sora Kasugano Arc
Advantages of the Omnibus Format
The omnibus format allows animation studios to work more quickly and efficiently with source material adaptations from dating simulation games and visual novels because it removes the need for writers to write around obvious plot issues involved with the protagonist and a potential harem that would go against the canon of the works they are based on.
With Key visual novel-based Clannad, for example, which was not aired in the omnibus format, the animation studio had to work in two other heroine's routes in separate single-episode original video animations, restricting romantic development with those heroines to 20-minute segments.