Monthly Shōnen Sirius

Kodansha launched Monthly Shōnen Sirius in May 2005 to carve out a space in the monthly shōnen market dominated by rivals like Weekly Shōnen Jump. Printed in perfect-bound B5 format and priced at 580 yen, the magazine targets young men with a specific mix of action, fantasy, science fiction, and romance. Editor Takashi Yamaguchi steered the publication toward high-concept narratives, particularly dark fantasy and isekai stories that set it apart from traditional adventure magazines.

The magazine found its commercial peak with That Time I Got Reincarnated as a Slime, which began serialization in 2015. Fuse's web novel adaptation became a multimedia empire boasting over 40 million copies in circulation, two anime seasons, and two films. Earlier hits included Sankarea: Undying Love (2009–2014) and Yozakura Quartet (2006–2023), both of which transitioned to television animation. Tsutomu Nihei brought his distinct biomechanical style to the pages with APOSIMZ (2017–2021) and the ongoing Tower Dungeon (2023–present).

Print circulation has steadily declined over two decades. The magazine moved 20,000 copies per issue in mid-2008 but dropped to 12,684 by 2013 and further to 8,917 in 2016. By the fourth quarter of 2025, sales had fallen to 6,983 copies. To combat this trend, Kodansha expanded its digital presence through the "Twi Siri" Twitter account for chapter releases and launched a digital-only spinoff called ARTEMIS by sirius in June 2025 aimed at female readers. A July 2025 sale offered volume 1s of titles like APOSIMZ for $0.99.

Current serializations feature Versus, a collaboration between ONE and Azuma Kyoutarou; Bless by Yukino Sonoyama; Bootsleg by Suzuhito Yasuda; Die Wergelder by Hiroaki Samura; and The Masterful Cat Is Depressed Again Today by Hitsuji Yamada. The latter received an Eisner Award nomination in 2024. Recent announcements include a dental spinoff of Cells at Work! debuting in October 2026 and a new series titled Itsuwari by Yasushi Baba in January 2026. [modifier]