Beyond the Boundary: Idol Trial (きょうかいのかなた アイドル裁判！～迷いながらも君を裁く民～, Kyoukai no Kanata Aidoru Saiban! ~Mayoi Nagara mo Kimi wo Sabaku Tami~, lit., "Beyond the Boundary: Idol Trial! Even as You Waver, the Nation Judges You~") is an idol-themed spinoff of the Kyoukai no Kanata anime series. It was released as a three-episode original net animation series uploaded to video streaming sites such as Nico Nico Douga and Youtube, starting from November 18, 2013, and portrays the four girls of the Kyoukai no Kanata series as "idol judges" who prosecute key characters of the series for questionable behavior. The final two episodes were included only on the seventh Bluray/DVD volume, which was released on July 2nd, 2014.
The miniseries is set on a small courtroom, where one character from the Kyoukai no Kanata series is put into trial for a particular trait that was found to be questionable. The defendant, which was given little time to defend oneself after instantly transported there, is given some time to interact with the idol judges, until the presiding judge appears and announces the charges against the defendant. After a short number where the courtroom transforms into a stage for the idol judges to perform their "judgment" dance, a verdict is given relevant to the charge.
The idol judges, Ai Shindou, Mirai Kuriyama, Mitsuki Nase and Sakura Inami, is depicted in super-deformed versions of themselves, dressed in a idol-style clothing under a black court dress, the latter of which is removed when they perform the song "Judgment Ja!". The ending song is Poppy no Kaerimichi, which is performed by Ai Shindou's voice actress, Yuri Yamaoka. Both songs are included on the Kyoukai no Kanata Original Soundtrack "Beyond the Melodies".
- Ai Shindou - The presiding judge of the idol trials, known for delivering the verdict with an innocent smile on her face. Those under trial easily notices her tendency to take advantage of her innocent looks and personality.
- Mirai Kuriyama - The bespectacled member of the idol judge group, known for her catchphrase "that's unpleasant". She is prone to panicking when confronted by things that she find unsettling.
- Mitsuki Nase - The member of the idol judge group with the sharpest tongue.
- Sakura Inami - The taciturn member of the idol judge group. Shows very little interest in participating in the idol trials, and is often scolded for Mirai for this.
- Akihito Kanbara - A 2nd year high school student in Nagatsuki High School. He is charged for "being gross", particularly due to his attraction to glasses in general.
- Shizuku Ninomiya - Teaches in Nagatsuki High School. She is charged for "being painful", which pertains to Shizuku's numerous attempts to look young in front of others (especially men).
- Hiroomi Nase - Mitsuki's older brother and a siscon. He is charged for "being indecent", and was given a swift verdict after showing up at the courtroom naked except for his scarf.
- Yayoi Kanbara - Akihito's human mother who comes to court late and dressed like a high school girl. She is charged for "being annoying", and her body is switched with Akihito's as punishment.
- Izumi Nase - Mitsuki and Hiroomi's older sister. She scares the judges so much that they declare her innocent. At the end, it is revealed that the trials were all part of Akihito's dream.