"Sensei is really going all out!" Unexpected person was the "inside person" of the costume at 'Blue Box' stage event

On December 21st, Koji Miura, the author of the manga 'Blue Box', reported on X that he had appeared at Jump Festa 2026 in a "Chinatsu-senpai" costume, sparking many voices of astonishment.

'Blue Box' is a comic series currently serialized in "Weekly Shonen Jump" (Shueisha), which delicately depicts the earnest dedication of life-sized characters pouring their hearts into club activities, and the subtle emotional shifts "when one falls in love with someone." The TV anime version was broadcast in two consecutive cours starting in October 2024, and a second season has also been confirmed for production.

Jump Festa 2026 was held at Makuhari Messe in Chiba Prefecture on December 20-21. At this event, on the 21st, a 'Blue Box' stage featuring the anime version's cast was held, and a costume of "Chinatsu-senpai," a cute, deformed version of the character Chinatsu Kano from the series, also appeared on stage.

After the event ended, Miura reported on X that he had been inside the "Chinatsu-senpai" costume. He revealed that in addition to appearing on stage, he had also participated in greeting fans, and that it was a surprise even to his co-stars, the voice actors, concluding with "I had fun interacting with the fans! Thank you very much!"

In response to this big surprise announcement that "the author was the person inside," fans' voices of astonishment poured in, saying "Isn't this an unprecedented surprise? (lol)" "As a fan, this is like a dream come true!" and "Sensei is really going all out!"

Additionally, fans who had unknowingly taken photos during the greeting expressed their joy, saying "So Koji Miura-sensei was right there with us" and "That means I took a two-shot with Miura-sensei."

(C) Kouji Miura/SHUEISHA, Blue Box Film Partners