Here are some factors that influence the length of an anime series:
* Source Material: The amount of content available in the original manga, light novel, or video game determines the potential length of an anime adaptation. Some stories have a limited number of chapters or volumes, leading to shorter series.
* Popularity and Success: If a show is successful and popular, it's more likely to receive a second season, extending the overall length.
* Production Costs: Anime production is expensive, and studios need to balance the budget with the potential audience. Shorter series may be a safer financial choice for some projects.
* Seasonality: Some anime are created for specific seasons, like summer or winter, and their episode count may be influenced by this.
* Story Structure: The narrative structure of the story might naturally lend itself to a shorter format, like a self-contained arc.
Funimation, like other anime distributors, acquires and licenses anime series based on the original production, not dictating the number of episodes. They might choose to split longer series into multiple seasons or release shorter ones as standalone series.
It's important to remember that the anime industry is diverse, and there are many different production models and approaches. The decision to produce a 13-episode series is not solely based on Funimation's policies.