Masaki Tsuzuki is a Japanese game planner, scenario writer, manga author, and lyricist, best known as the original creator of the Magical Girl Lyrical Nanoha franchise. His career began in the late 1990s within the adult game (eroge) industry, where he was a key member of the brand ivory. During this period, he was involved in the planning, scripting, and illustration for numerous games, notably the Triangle Heart series, including Triangle Heart 3: Lyrical Toy Box, which directly laid the groundwork for what would become the Magical Girl Lyrical Nanoha universe.

Tsuzuki's breakthrough into mainstream animation came with Magical Girl Lyrical Nanoha in 2004. He served as the original story creator and screenwriter for the series, a role he would continue across its many sequels, including Magical Girl Lyrical Nanoha A's, StrikerS, and the film adaptations such as Magical Girl Lyrical Nanoha Detonation and Magical Girl Lyrical Nanoha Reflection. The Nanoha franchise distinguished itself from traditional magical girl narratives by incorporating elements of science fiction, mecha anime tropes, and a focus on tactical combat, a direct result of Tsuzuki's creative vision.

Following the success of Nanoha, Tsuzuki created another original anime, Dog Days, which first aired in 2011. The series, set in a fantastical world where conflicts are resolved through non-lethal sports competitions, features a lighter tone and adventure-focused narrative. He continued to expand this universe with subsequent seasons, including Dog Days' and Dog Days'' (Dog Days Double Dash). Tsuzuki also created the original anime Extreme Hearts, which premiered in 2022. The story is set in a near-future where "Hyper Sports" are popular and follows a high school singer who becomes involved in these athletic competitions. Tsuzuki is credited with the original story and scripts for the series.

In addition to his anime work, Tsuzuki has been a prolific manga author and original creator, primarily for stories set within the Nanoha universe. His manga credits include Magical Girl Lyrical Nanoha ViVid, Magical Girl Lyrical Nanoha Force, and Original Chronicle Magical Girl Lyrical Nanoha The 1st, among many others. He has also authored the manga adaptation for Dog Days. His involvement often extends to writing lyrics for character songs and theme music associated with his properties.

Tsuzuki's artistic identity is characterized by a focus on creating expansive, interconnected universes with a large cast of characters. His writing style is noted for its emphasis on character relationships and personal motivations over complex world-saving ideologies, often focusing on sincere emotions as the primary driver for character actions. Furthermore, he is known for his detailed scripts, which contain extensive descriptions of action and movement, sometimes exceeding the standard page count for a typical television episode. In the industry, he is a significant figure as the founder of a major multimedia franchise and is a member of the animation studio Seven Arcs, with which he has closely collaborated for many of his projects.