这是一部人气儿童向动画的剧场版第3弹，描述了外表看起来很臀部，但推理和举止却很绅士的名侦探“小屁股”的活跃模样。一年到头风吹的“苏霍莱岛”，收到…

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本作改编自田中阳子和深泽将秀双人搭档所创作的绘本，以可爱的大头屁股侦探，与搭档小狗布朗一起，通过犯罪现场的一系列蛛丝马迹，推理追踪犯人的故事……

トロルさんの絵本が原作の人気アニメ「おしりたんてい」とNHKの科学番組「コズミック フロント」がコラボした新作スペシャルアニメ「おしりたんていコズミックフロント」が3月にNHK・Eテレで放送されることが分かった。第1弾「コズっとなぞとき！きえたきょうりゅうかせき」が18日午後2時45分、第2弾「コズっとなぞとき！うちゅうのおおどろぼう」が25日午後2時35分に放送。

Mystery of the Ladybug Ruins. Here comes the second piece of “Butt Detective" jumps to the big screen. This is an adventurous action film that tells the story of the Butt detective and his father Butt Dandy discover the mystery of the ancient ruins together! One day Butt Detective received a commission from his father's Butt Dandy, which is going to the Ladybug Ruins to investigate into a case. According to the rumors, the hidden treasure in the ruins, possibly could save the continuous drought in the dim dim village. Butt Dandy and a baby panda called Tan arrived to the site in advanced, however someone who wants to steal the treasure are already onto them. Moreover, the phantom thief U delivered a criminal notice at the same time. Butt Detective follows the footstep of Butt Dandy, while unraveling various mysteries in the ruins!

The Case of the Courageous Curry. On a sunny afternoon, Butt Detective and his assistant Brown are enjoying a leisurely afternoon tea at the cafe. Mr. Walter, the manager of a new curry restaurant in town, walked in with a large shopping bag. At this time, he found that the spices he had just bought, “Piriritokikku", an essential spice for curry dishes, had disappeared from his shopping bag. “You can't make curry without the spices! There is no way to open the business on schedule!” While Mr. Walter was devastated and distressed, Butt detective step forward, his remarkable reasoning mind is ready to solve the disappearance of the curry spices.

本作改编自田中阳子和深泽将秀双人搭档所创作的绘本，以可爱的大头屁股侦探，与搭档小狗布朗一起，通过犯罪现场的一系列蛛丝马迹，推理追踪犯人的故事……