長谷川の兄さんは暇である

From Author Wars - https://authorwars.com/publications/chang-gu-chuan-noxiong-sanhaxia-dearu-740941.html

Overview:

Title: 長谷川の兄さんは暇である
Author: 大川慶
Year: Unknown
Publisher:
Binding: unknown
Type: Novel
Title Reference: 長谷川の兄さんは暇である
Notes: Not published as of 2019-10-24, though it was a finalist for the 2018 Japan Fantasy Novel Award, so it may still be published at some point.