Maruko Tanaka is recognized as an original creator in the manga and anime industry, primarily known as the co-author of the story that inspired the series Aru Hi Inu no Kuni kara Tegami ga Kite. This work, whose title translates to One Day a Letter Arrives from the Dog Kingdom, began as a novel written by Tanaka together with Yūkō Matsui, first published in 2009. The story revolves around a touching concept where deceased dogs are able to write and send a single, heartfelt letter to their former owners from a place known as the dog kingdom.

The novel was subsequently adapted into a manga series, which was illustrated by manga artist Sayuri Tatsuyama, known for works such as Happy Happy Clover. This manga adaptation began serialization in Shogakukan's Ciao magazine in July 2012, first as a one-shot and then as a full serialized work due to its popularity. Tanaka, alongside Matsui, is consistently credited for the original concept and scenario on which Tatsuyama's manga is based. The manga has been compiled into several volumes and was also released in French by the publisher Glénat under the title Le paradis des chiens.

In 2015, the work received an anime adaptation. An original anime DVD (OAD) was produced and bundled with the September issue of Ciao magazine. This animated episode adapted a specific chapter from the manga titled P-chan ~Hitomi wo Tojireba~. The anime was promoted as a moving story about a dog named P-chan who was abandoned by his owner. Through this progression from original novel to manga to anime, Maruko Tanaka’s role is that of a foundational story creator, with her narrative concept being adapted into different media by other primary creators.