Director Kim Han-min who helmed “The Admiral: Roaring Currents” (2014), South Korea’s biggest hit of all time with 17 million admissions, spent the last decade producing a trilogy on Adm. Yi Sun-sin, one of the most revered figures in Korean history.

On Wednesday, the epic finale “Noryang: Deadly Sea” opened in theaters.

“I’m just not ready to leave Adm. Yi Sun-sin. To borrow his word, it was definitely a blessing from heaven – 'cheonhaeng' – that I was able to produce and complete this trilogy project,” Kim told The Korea Herald in an interview in Seoul on Tuesday.

“Noryang” features a lot of sophisticated computer graphics than its first installment “The Admiral: Roaring Currents” and its prequel “Hansan: Rising Dragon.”

“To vividly portray the night battle scene, we put tremendous focus on mapping out the scene using computer graphics, so the audience won't get tired of following this fierce battle. Because the scene involves a lot of fire, water as well as gunfire, we desperately needed a set that could satisfy all our needs and it was the ice skate rink in Pyeongchang, Gangwon province,” said Kim.

According to Kim, over 800 staff from 25 CG companies participated in the 100-minute battle scene. Some 30 billion won ($22 million) was spent on the battle sequence alone, involving 100 ships, to convey the largest-ever naval battle in Asian history. It was also the only battle that took place at night during the seven-year Japanese invasion of Korea in 1592.

Kim chose different actors for the admiral in each of the films in the trilogy: Choi Min-sik in the first installment, Park Hae-il in the second and Kim Yoon-seok for the finale.

“In ‘The Admiral: Roaring Currents,’ I wanted to convey Adm. Yi’s courageous leadership. In ‘Hansan,’ a young Yi Sun-sin’s cleverness and strategic mindset had to be portrayed. The finale had to show Yi Sun-sin’s wisdom and insight as a leader and a man,” Kim explained.

“It’s not that I didn’t think of Choi playing Yi Sun-sin throughout the trilogy, but he said he spent so much energy playing Yi during the first installment. Then I decided that maybe I should cast different actors to show Adm. Yi’s different tactics for naval battle,” he added.

Kim said he still reads "Nanjung Ilgi," the war diary Yi wrote, whenever he is stressed, saying it gave him "great encouragement."

“I can find many friendly aspects of him through this diary" and got to know him on a deeper, more personal level, beyond his role as a military leader, he said, adding that he also reads the diary when he can’t go to sleep. “His words and sentences are very calm and make me easily fall asleep,” he said, jokingly.

Kim also hinted that although his decadelong project on Yi has come to an end, that doesn’t mean that he will stop producing more stories about him.

“Why can’t I make a story on Adm. Yi Sun-sin in which he doesn’t appear? I’m just not ready to let him go," Kim said.

"Also, Korean history offers so many things to think about for people these days, when it’s told through period flicks. When you look at Korean history, there are moments when mishaps are repeated because certain historical events have not been concluded well. I think Yi Sun-sin is kind of a figure who reminds us to not forget such a lesson."