Seok Hannah, or by her stage name, Hannah debuted as a soloist on December 16, 2019, with her song, Cheers! (짠!) on her 1st mini-album, Cheers! The debut has met some controversy on the music video, that she, an underage/minor went to a bar, and hold an alcoholic drink. This violated the laws of the safety of alcohol drinking and they told, that this may boost the influence of underage drinking. The CEO issued an apology for this issue, and the hype of this has been going down, after there is no scene that helps the use of underage drinking, and they also counter the fact, that Hannah wasn't showing any signs of drinking alcohol. The debut, however, seems to be successful. However, she didn't appear on music shows.

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She appeared on the 2019 Season Greetings special song "Christmas", with along other Boo Entertainment artists.

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She was also nominated on the 2020 Sunset Music Awards, and she won the "Rookie of The Year" award.

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She appeared also as a contestant on the IDREAM30 survival show, created and managed by YJ Entertainment (now PLAY Entertainment). She finished the competition in 7th place and was a member and the main vocal of the FAN7ASY. She also appeared on the FAN7ASY's debut music video, Bungee!. Unfortunately, after FAN7ASY's debut, the entertainment chose to disband early, and Hannah decided to go back as a soloist.

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She came back with her song, Blue Moon on her 2nd mini-album; Moon, Stars, and You on April 10, 2020. The comeback received popularity and success, after being on IDREAM30. After her promotions, she proceeds to do Asia's Next Top Model (Monthly Idol).

She finished at Top 5 and was eliminated after. She proceeds also to be the dance mentor on IDREAM18, the second season of IDREAM30. She also became the dance mentor of Go!Idols, the survival show of Jewel Entertainment. Both of the shows mentioned have canceled (the Go!Idols) and discontinued (IDREAM18) respectively.

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She announces her fandom name; IBLUE, her official lightstick, and her official logo altogether on May 19, 2020.

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On July 7, 2020, Hannah came back with her song, Pporappippam, on her 3rd mini-album, Purple Heart.

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On November 27, 2020, Hannah came back with her 1st digital single, Shining Light. She also introduced her "members". One of the "member" Seohyeon, played an electric guitar as a part of an acoustic performance of Shining Light. 4 out of 9 "members" was announced to be left from the company, and was replaced with 4 new "members".