The anime that cost the most funds is "Attack on Titan," which had a budget of approximately $8 million per episode. This high cost was primarily due to the complex animation, detailed character designs, and extensive production process required to bring the intricate world and story to life.

The reason for the high budget of "Attack on Titan" lies in several factors. Firstly, the anime is known for its high-quality animation, which requires a large number of skilled animators and artists. The detailed character designs and the vast, detailed world of "Attack on Titan" demand a significant amount of time and effort to create. Additionally, the complex story and action sequences require precise and detailed animation to maintain the visual impact and emotional resonance with the audience.

According to a report by Variety, the production company behind "Attack on Titan," MAPPA, invested heavily in the animation process, using advanced techniques and technology to ensure the highest quality. This included the use of motion capture for certain scenes, which added to the realism and depth of the characters' movements.

Furthermore, the success and popularity of "Attack on Titan" also contributed to its high budget. The anime became a global phenomenon, attracting a massive fanbase and generating significant revenue through merchandise, streaming rights, and other licensing deals. This financial success allowed the production company to allocate more resources to the project, ensuring its high-quality production.

In conclusion, "Attack on Titan" is the anime that cost the most funds due to its intricate animation, detailed character designs, and the extensive production process required to bring its complex world and story to life. The high budget was justified by the anime's success and the quality of its production, which has since set a precedent for other high-budget anime productions.