Photo/Illutration "That Time I Got Reincarnated as a Slime the Movie: Scarlet Bond" (Provided by Bandai Namco Filmworks Inc.)

The wildly popular self-published Web novel "That Time I Got Reincarnated as a Slime" is hitting the big screen for the first time.

Commonly known as "TenSura," the series' protagonist is Rimuru, a former corporate worker who is reincarnated as a slime in a different world.

He acquires special skills and makes friends with other monsters.

The series eventually sold 30 million copies of light novels and comic books, while it spawned TV anime and video game adaptations.

The feature film, titled "That Time I Got Reincarnated as a Slime the Movie: Scarlet Bond," is based on an original story provided by author Fuse.

Having pushed his way to become the king of his own nation, Rimuru confronts a conspiracy involving a small country called Raja that has flourished on gold mining.

"The story and battle scenes are so richly immersive and fired up that they are worth the movie experience," said Miho Okasaki, who voices Rimuru.

Okasaki was cast as Rimuru in 2018 at age 19 after she made her voice actress debut the previous year. It was her first protagonist role in an animated TV series.

"I was worried about the role because he was a 37-year-old man in his previous life and is now a slime," she said. 

Despite Rimuru's slightly built appearance and gentle manners in his human form, he boasts an invincible strength.

"He cares for the Queen Towa of Raja when she is in distress while he trusts his crew and lets them fight battles, and it is this mental maturity that makes Rimuru who he is," Okasaki said. "A sense of security Rimuru provides and a sense of expectation that makes us wonder what will happen next are the charms of 'TenSura.'"

The movie is currently showing nationwide.