A booklet packaged with Harta volume 17 at select stores. It's an anthology of one-shots centering on the theme of beautiful boy. (Source: Natalie, translated)

Japan has yet to become one unified country. A sudden cease-fire prevails in the fighting between the Yamato Imperial Court and the native Emishi people over Japan's northeastern Tohoku region. An Imperial Court envoy visits Aterui, the chief of a great Emishi tribe. The envoy who calls himself Sanekage proclaims, "Let's go on a journey to hunt a demon together." A demon created by a shōmoji entertainer in the Imperial Court had suddenly started attacking people indiscriminately. Aterui had no reason to lend a hand to his careless enemies, but he decides to embark on this journey due to Sanekage's offer related to revenge for Aterui's wife. (Source: Anime News Network) *Note: Includes 3 extra chapters.*

Corporate slave goes to another world, creates a restaurant in a dungeon, then gets hailed as history's strongest demon king as a result. Source: MU

Originally published in the Shounen Club Magazine of July 1934, page 158.