Monolith Soft is a video game development company who are responsible for the Project X Zone series. The company was formed by Tetsuya Takashi who is responsible for the Xeno franchise (Xenogears, Xenosaga and Xenoblade Chronicles). The company was made of former Squaresoft (now Square Enix) employees who worked on Xenosaga within Squaresoft.
Monolith Soft was acquired by Namco (now Bandai Namco) as a video game development subsidiary for the company. This partnership resulted in the Xenosaga series and Namco x Capcom (the spiritual predecessor of Project X Zone). Namco traded its shares of Monolith Soft to Nintendo resulting in Monolith Soft being a video game development subsidiary for Nintendo. This reformed corporal partnership resulted in the critically acclaimed Xenoblade Chronicles franchise and the start of the Project X Zone series.
Because Monolith Soft are the developers of the Project X Zone series, all the original characters and story elements are created by them. Despite this, Bandai Namco have ownership rights of the Project X Zone as the franchise started as Namco x Capcom without Nintendo’s affiliation.