1. "Ojisama to Marshmallow" by Reiko Momochi: This manga, serialized in the "Petit Comic" magazine, faced lower sales compared to other titles in the same magazine.
2. "Ushio to Tora" by Kazuhiro Fujita: Despite its anime adaptation and critical acclaim, "Ushio to Tora" did not achieve significant commercial success in Japan, with sales below expectations.
3. "Innocent" by Shinichi Sakamoto: While known for its intricate artwork, "Innocent" did not garner high popularity in Japan compared to some of Sakamoto's other works.
4. "Dorohedoro" by Q Hayashida: Though receiving praise for its unique art style and narrative, "Dorohedoro" had a limited print run and experienced relatively lower sales in Japan compared to other popular manga series.
5. "Moyashimon" by Masayuki Ishikawa: This manga focused on microbiology, and despite scientific accuracy and a devoted fanbase, it did not achieve widespread recognition in Japan.
6. "Parasyte" by Hitoshi Iwaaki: Although "Parasyte" later gained international recognition and an anime adaptation, it faced initial difficulties in gaining traction in Japan, with low initial sales.
7. "The Promised Neverland" by Kaiu Shirai and Posuka Demizu: While initially popular, the second half of the manga faced criticism for its narrative direction, leading to a decline in popularity in Japan toward its conclusion.
It's important to note that the definition of "least popular" can be subjective and based on relative comparisons. Other manga series might have also experienced lower popularity or faced challenges in attracting a wide readership in Japan.