Case Closed: Conan and Heiji and the Vanished Boy
Meitantei Conan: Conan to Heiji to Kieta Shounen · 名探偵コナン: コナンと平次と消えた少年
Synopsis
Conan and Ran are visiting Heiji and Kazuha in Osaka but while they are touring around they come across a group of three kids that look like Ayumi, Mitsuhiko, and Genta. The group are looking for their missing friend and Conan agrees to help. (Source: Anime News Network)
Studios: Shogakukan-Shueisha Productions, TMS Entertainment
Source: MANGA