River Where the Moon Rises

• Kim So-hyun as Princess Pyeonggang / Yeom Ga-jin
  • Heo Jung-eun as teen Princess Pyeonggang[13]
  • Jung Yoon-ha as young Princess Pyeonggang

A princess determined to be first Queen of Goguryeo.

• Ji Soo as On Dal
  • Seo Dong-hyun as young On Dal[13]

A peace-loving, pure man who goes against his principles in order to protect Princess Pyeonggang.

• Lee Ji-hoon as Go Geon
  • Park Min-sang as young Go Geon[13]

An elite general who was perfect in any way and longed to make Pyeonggang his.

• Choi Yu-hwa as Hae Mo Yong

A woman who desired to take control of Gorguyeo and play with it as she wanted. She fell in love with Go Geon.

• Wang Bit-na as Jin-bi, the crest of King Pyeongwon.[14]
• Lee Hae-young as Gowon Pyo, a Gyerubu Gochuga a cunning and elaborate politician who boasts a brilliant speech and excellent showmanship. With the conviction that his family should become King of Goguryeo, he takes the lead to dethrone the reign of King Pyeongwon.[14]
• Kim Pub-rae as King Pyeongwon, was originally a benevolent and generous king, but he has gradually changed into a sensitive and suspicious personality. Since then, he has been playing around with Gowon Pyo's tactics and is keeping the palace his.[14]
• Hwang Young-hee as Sa, the nanny of Ondal. A non-violent pacifist who values people's lives most importantly, and has a tremendous influence on Ondal's beliefs and ideas.[14]
• Kim Hee-jung as Tarajin, a killer who lives with her twin brother Tarasan, in Dorim-hyang, where people abandoned in Goguryeo gather and Princess Pyeonggang's love advisor.[15]
• Yoon Joo-man, as Ko Sang-cheol, Gowon Pyo's right arm man.[16]
• Heo Yool as Wol-i, a Baekje refugee and an influential figure in the ghost village. She has a one-sided crush on Ondal.[17]
• Jung Dong-geun as Il-yeong, Go Geon's escort warrior.[18]
• Ki Eun-se as Hyun-bi, one of King Pyeongwon's concubines.[19]
• Ahn Shin-woo as Kim Pyeong-ji, a friend of King Pyeongwon and a servant of Goguryeo. He is a person who does not check his family because he does not have much to see, has no property, and even has no family to protect[20]
• Kim Jung-young as Gong-son, nanny of Princess Pyeonggang. She is a loyal person who is guarding the empty Gongju Palace alone, hoping that Princess Pyeonggang, who disappeared 10 years ago will return alive, and then becomes a shadow of Pyeonggang after Pyeonggang comes back alive.[21]
• Jung Eun-pyo as Uhm-deuk, father of Uhm Ga-jin.[22]
• Ryu Ui-hyun as Tarasan, a talkative but clumsy Princess Pyeonggang's best friend and Tarajin's twin brother.[23]
• Park Sang-hoon as Prince Go-won, Princess Pyeonggang younger brother.[24]
• Son Woo-hyuk as Taegam, an eunuch who is a close aide to the King Pyeongwon and the head of eunuchs.[25]

• Kang Ha-neul as General On Hyeop, the father of Ondal and the head of the Sunnobu region in Goguryeo. His is a dutiful leader who fulfills his responsibilities for his country and his people. Embodying a sense of charisma and righteousness, he is a revered general of the people who receives support and loyalty from the masses.

Early working title of the series is Cut to the Heart (Korean: 마음에 베이다; RR: IMaeume beida).[26]

The series, based on Choi Sagyu's novel Princess Pyeonggang.[4] The novel shows a different perspective on Princess Pyeonggang as an outstanding leader to her country and people, breaking the image of a crying princess and a present-looking wife in the Goguryeo folktale Pyeonggang and Ondal.[27][28] Choi took 25 years for the novel to be completed.[4] It is directed by Yoon Sangho who had directed other works such as Saimdang, Memoir of Colors, Different Dreams, Kingmaker: The Change of Destiny and written by Han Ji-hoon who previously wrote Time Between Dog and Wolf, Temptation and Woman of 9.9 Billion.[29] The drama is produced by Victory Contents.[30]

On January 27, 2021 Viu revealed River Where the Moon Rises as its latest Viu Original. Virginia Lim, Viu’s chief content officer commented: "With an exceptional script and amazing talent, River Where the Moon Rises is not to be missed."[10]

The production company, Victory Contents conducted a public audition for the drama from August 3–4 for it to be produced in the second half of 2020. The performers recruiting are male and female actors from 1987 to 2005, skilled in martial arts and sports or have experience in dramas, movies, and performances.[26] On October 30, Victory Contents announced the winner of The Next public audition, actor Jung Dong-geun. He was chosen through 1:1000 candidates.[18]

On August 25, Sports Seoul reported that Son Ye-jin was in talks to star in the series.[31] Following the reports, a source from Son's agency MS Team Entertainment shared, "It's one of the projects she has received offers for, and nothing is decided yet." They continued, "She is currently spurring her advance into Hollywood by affirming her appearance in the Hollywood film The Cross by Andrew Niccol."[32] The same day, it was also reported that Kang Ha-neul was cast as On Dal,[33] but turned down the offer due to a scheduling conflict on September 21.[34] The following day, Kang's agency confirmed his special appearance as General On Hyeop.[35]

On October 5, it was reported that Kim So-hyun has been cast and confirmed as the protagonist of the drama.[11] On October 13, it was reported that Ji Soo had received an offer as the role of Ondal, the male protagonist in the drama but was still reviewing it.[36] On October 22, Ji Soo is confirmed to be acting as the male lead On Dal, with Lee Ji-hoon and Choi Yu-hwa joining the cast.[37] The script reading was held on October 23, 2020.[8][38]

The series reunites actors Kim So-hyun, Ji Soo and Hwang Young-hee who previously acted together in the drama Page Turner. This marks the third collaboration of Kim So-Hyun with Hwang Young-hee after 2016 series Page Turner and film Pure Love, and second collaboration with Jung Eun-pyo in 2012 Moon Embracing the Sun. It also reunites Kim So-Hyun and Kim Hee-jung who previously worked together in 2015 series Who Are You: School 2015.

On November 23, the production of The Moon Rising River was suspended as a direct result of the COVID-19 pandemic. It was reported that a supporting actor was identified as close contact with a COVID-19 carrier. Ten crew members who came in contact with the person also underwent voluntary COVID-19 testing. OCN's The Uncanny Counter which shares the set with the series decided to cancel their press conference.[39] On November 24, the extra's result was confirmed positive but all affiliated cast and crew members have tested negative including ten staffs that had close contact with the supporting actor. For safety, the production crew practice self-isolation for one or two more days, observe the situation and resume shooting.[40]