Masashi Kishimoto's Naruto is one of the most popular manga series in the world, having sold over 220 million copies worldwide, per Anime News Network. The series ended on Nov. 10, 2014 after 15 years of production, and Kishimoto recently talked to Entertainment Weekly to discuss the success of Naruto.

"What made Naruto successful was the globalization of manga, and the fact that all over the world, fans can enjoy and read manga even though the reading order is different than what people are used to," Kishimoto said.

"I was actually able to work on Naruto and bring it to a successful conclusion. That is one of the things I'm most proud of. And I had absolutely no idea that it would ever be a success, much less a success of the level of what it is now," he added.

The 41-year-old manga artist also said that the most challenging moment while working Naruto was the creation of Pain and its plot. He had difficulty drawing Naruto convincing Pain verbally to change his ways that it cause him to hurt his back.

Kishimoto added that he worked through the pain and did not take a break making the plot. He also mentioned that the art for that arc looked very rough because he was working in pain and could not focus on his work.

As for his next project, he told Entertainment Weekly that he is first planning a trip to Hawaii and spend some time with his wife and kids. He added that he still has no idea for his next project.

However, in an interview with a Japanese Magazine via Kotaku last August, Kishimoto revealed that he was already thinking of his next manga project. "I'm thinking I'm going to do science-fiction. It hasn't all been worked out, and I haven't showed my editor yet, but I've already designed the characters," he said.

The Okayama-native added that his new manga will be released monthly. Kishimoto noted the difficulty he endured finishing Naruto because it had a weekly deadline. He's also more interested in doing his monthly manga for digital publication Shonen Jump Plus because it offers more freedom with page counts and publication dates.

During the 15 years of Naruto, it has created multiple properties that included two anime series, movies, music, video games, novels, trading card game, art and guide books, figurines and toys. There is no known value of how much the Naruto franchise is worth, but Kishimoto has an estimated net worth of $20 million, according to Celebrity Net Worth.