Question: Who starred in South Korean film that "Pencil" was based on?
Context: No Regret () is a 2006 South Korean film and the feature film directorial debut of Leesong Hee-il, based on his earlier short "Good Romance".  "No Regret" is also regarded as "the first 'real' Korean gay feature", (although earlier South Korean films, such as "Road Movie", released in 2002, have dealt with gay relationships), and is also the first South Korean feature to be directed by an openly gay Korean filmmaker. Pencil is a 2016 Indian Tamil mystery thriller film written and directed by debutant Mani Nagaraj and produced by S. P. Ragavesh.  The film is based on South Korean film "4th Period Mystery" released in 2009.  The film features G. V. Prakash Kumar and Sri Divya in the lead roles, with the former also composing the film's music.  The film was released on 13 May 2016. 4th Period Mystery (), released internationally as The Clue, is a 2009 South Korean thriller film starring Yoo Seung-ho and Kang So-ra. Tell Me Something () is a 1999 South Korean Thriller-Horror-Crime film directed by Chang Yoon-hyun.  It was an early South Korean film to find success abroad as part of the Korean Wave, and was selected to appear in the 2001 New York Korean Film Festival. The Vermilion Pencil is a 1922 silent film produced and distributed by Robertson-Cole, later a part of Film Booking Offices of America.  It is based on a 1908 novel by Homer Lea called "The Vermilion Pencil".  The film starred Sessue Hayakawa, Ann May, Bessie Love, and Sidney Franklin.  It is now a lost film. Green Fish () is a 1997 South Korean film.  It was the first feature-length film directed by Lee Chang-dong, who also co-wrote the screenplay.  Lee had previously been known as a novelist and high school teacher.  The film stars Han Suk-kyu in one of his first major film roles.  It was the eighth highest-attended South Korean film of 1997. My Little Brother (, lit.  "Yes, Family") is a 2017 South Korean film and the directorial debut of Ma Dae-yun.  It is the first South Korean film to be distributed by The Walt Disney Company. Jeong Jae-heon (Korean: 정재헌 ; born April 18, 1975) is a South Korean voice actor and actor.  He joined Munhwa Broadcasting Corporation's voice acting division in 2002.  After being a freelancer, Jae-heon made a brief appearance on a 2005 South Korean film "Quiz King", playing his role as a television news reporter.  The voice actor became popular with his dub of Kiyomaro Takamine on "Zatch Bell! ", which has been one of his signature works.  He gained popularity also by replacing Adam Rodriguez on "", and Archie Kao on "".  In late 2011, Jae-heon once was on stage, portraying Lee Mong-ryong in a South Korean charity play "Hyang-dan, Fly".  He has recently been known for his voicing Shota Kazehaya on the Korean dub of a Japanese television animation series "From Me to You", which made many fans of Jae-heon call him 정재하야 (Jeong-jae-ha-ya, a compound word formed from "Jeong Jae"-heon and Kaze"haya"). Seopyeonje () is a 1993 South Korean musical drama film directed by Im Kwon-taek.  Its story tells of a family of traditional Korean pansori singers trying to make a living in the modern world.  The film was originally expected to only draw limited interest, and was released on only one screen in Seoul.  At the height of its popularity, it was shown on only three screens at once in the entire city of over 10 million.  Nevertheless, it ended up breaking box-office records and became the first Korean film to draw over a million viewers in Seoul alone.  When it was released, "Sopyonje"'s success also increased interest in pansori among modern audiences.  The film was acclaimed critically, both in South Korea and abroad, getting screened in Cannes Film Festival and winning six Grand Bell Awards and six Korean Film Critics' Awards. Fighter in the Wind (Korean: 바람의 파이터 ) is a 2004 South Korean film.  It is based on the Japanese book "Karate Baka Ichidai" which is a fictionalized account of karate competitor Choi Yeung-Eui (최영의, 崔永宜) who went to Japan after World War II to become a fighter pilot but found a very different path instead.  He changed his name to Masutatsu Oyama (大山倍達) and went across the country, defeating martial artists one after another.  This film concentrates on the period when he is still young, and developing his famous karate style, Kyokushin.  The film was the seventh highest grossing Korean film of 2004 with 2,346,446 admissions sold nationwide.
Answer: Yoo Seung-ho and Kang So-ra