The Case Book of Arne (アルネの事件簿, Arune no Jikenbo) is a Japanese mystery adventure game by Harumurasaki (Murasaki), with character designs by Harutarō.

It was created using RPG Maker and was originally released as a freeware via the Vaka Game Magazine website in November 2017.

A manga adaptation with art by Soraho Ina was serialized in Media Factory's shōjo manga magazine Monthly Comic Gene from November 2018 to March 2022 and was collected in four tankōbon volumes.

[2] The manga's chapters were collected into four tankōbon volumes from April 27, 2019, to March 26, 2022.

The series is written by Harumurasaki, with Harutarō returning from the game to design the characters.