Kim released his second solo song "Abyss" via SoundCloud and YouTube on December 3, 2020. An acoustic ballad inspired by his feelings of anxiety, doubt, and burnout, Kim co-wrote and co-composed the track with RM and record producers Bumzu and Pdogg. In a post to the official BTS blog, Kim spoke about his insecurities regarding music and how those darker emotions drove him to write and release the song. In October 2021, Kim sang the main theme for the TvN drama series Jirisan. Titled "Yours", the single's release was accompanied by a music video featuring footage from the show. On December 4, Kim released the short trot-style song "Super Tuna" via SoundCloud as a gift to fans in celebration of his 29th birthday. It quickly went viral after an accompanying performance video was posted on the BTS YouTube channel that same day. The video ranked first on YouTube's World Popular Music Video for eight consecutive days and trended in 56 countries, including Korea, Peru, and Singapore. A subsequent dance challenge arose on TikTok, with videos using the sound receiving over 141.8 million cumulative views in 10 days. In August 2022, Kim collaborated with Nexon as a special game developer for MapleStory. The project was chronicled in the form of a two-episode mini web series, Office Warrior Kim Seok Jin, published to MapleStory Korea's YouTube channel. On October 21, "Tonight", "Abyss", and "Super Tuna" were made available on streaming services worldwide as official singles under Kim's name. All three songs subsequently simultaneously occupied the top three of the November 5 issue of the World Digital Song Sales chart, making Kim the third soloist in the history of the chart to do so. Kim released his debut solo single "The Astronaut", which he co-wrote with the British rock band Coldplay, and an accompanying music video on October 28. He performed the song live with the band later that same day in Buenos Aires during their Music of the Spheres World Tour; the show was broadcast live to cinemas worldwide in over 70 countries. The single earned Kim his first solo entry on the Billboard Hot 100 at number 51 and his third number one on the World chart. Artistry Kim is a tenor and plays the guitar. In the 2019 novel BTS: The Review, members of the Grammy panel praised Kim's stable breath control and strong falsetto, calling it a "silver voice".