Masahiro Totsuka is a Japanese manga artist and original creator, known primarily for his work in comedy and seinen manga. His professional alias is written in Japanese as 土塚理弘, and he originates from Nagano Prefecture. Totsuka began his career in the late 1990s, gaining early recognition when he won a semi-grand prize at the 8th Enix 21st Century Manga Awards at the age of 19 for his work Kiyomura-kun to Suginokouji-kun, which also became his debut publication in 1999.

Totsuka is most widely recognized as the original writer for the popular manga and anime series Bamboo Blade. He provided the original story for Bamboo Blade, which was illustrated by Aguri Igarashi and serialized beginning in 2004. The success of this series led to a television anime adaptation that aired from 2007 to 2008. This work significantly raised his profile within the industry and demonstrated his skill for combining sports-themed narratives with character-driven comedy.

The creator is also known for the gag manga Kare Baka: Wagahai no Kare wa Baka de R. Totsuka is credited as the original creator and writer for this series, which features art by Saki Azumi. The manga is a love comedy centered on a high school girl named Akomi and her boyfriend, Ponta Ninomiya, who is described as a massive idiot with no redeeming qualities other than his handsome face. The series follows the absurd and humorous everyday lives of the couple. Kare Baka was previously serialized under the title Wagahai no Kare wa Baka de Aru in Hakusensha's Young Animal Island magazine from 2012 to 2014, before being re-serialized in its final form starting in 2015.

In 2015, it was announced that Kare Baka would receive an anime adaptation. The result was an original net animation (ONA) series directed by Akiko Seki and produced by Sakura Create. The anime consisted of eight short episodes, each approximately five minutes long, which were streamed online from October 2015 to January 2016. The cast included voice actors such as Juri Kimura as Akomi Natsuki and Daisuke Namikawa as Ponta Ninomiya.

Throughout his career, Totsuka has demonstrated a strong affinity for comedy and gag manga, a genre he has worked in since his debut. He has also shown a capacity for long-form fantasy storytelling with earlier works like Material Puzzle, which he serialized in Monthly Shonen Ganggang starting in 2002. A recurring element in his works is the appearance of cats as background motifs, often referred to by readers as the Totsuka Cat. His artistic identity is also marked by a focus on clean, character-driven humor without relying on fan service, a choice reportedly made during the Bamboo Blade adaptation when he declined suggestions to feature female characters in swimsuits, feeling it would not suit the story.

Totsuka has also been noted for his collaborative process. For Kare Baka, he worked directly with illustrator Saki Azumi, a partnership that had previously produced the Bamboo Blade B spinoff manga. This collaborative model, where Totsuka provides the original narrative and another artist handles the illustrations, is a significant part of his creative output. His significance in the industry rests on his ability to create enduring comedic premises that translate successfully into other media, most notably with Bamboo Blade, and to maintain a consistent and prolific career as a writer and original creator in Japanese manga publishing.