"Good Day" went on to spend five consecutive weeks at the top of South Korea's Gaon Digital Chart, and in 2019, it was ranked number one on Billboard's "100 Greatest K-Pop Songs of the 2010s" list.

[2] With the success of her 2011 albums, Real+ and Last Fantasy, IU established herself as a formidable force on the music charts of her native country and further cemented her girl next door image as Korea's "little sister".

[11] Aside from her music career, IU has ventured into acting and hosting radio and television shows, starting with a supporting role in the hit teen series Dream High (2011).

[40] The song was noted for its stark contrast in musical style to "Lost Child", which was described as a "heavy" and "dark" ballad compared to the 1980s "retro sound" of "Boo".

[41][42] Deemed as a "strategic" transformation, the dance choreography, stage costume and hairstyle shown in live performances were used to emphasize her youthfulness and project a "cute" image.

[45] As her popularity began to rise, IU made more frequent appearances on variety shows, performing on Star Golden Bell, Kim Jung-eun's Chocolate, and You Hee-yeol's Sketchbook.

Her acoustic covers of other artists' songs such as Girls' Generation's "Gee", Super Junior's "Sorry, Sorry", and BigBang's "Lies" featured in these live performances gained tremendous interest online.

Admitting that she was doubtful about her readiness to take on acting, IU remarked that she gained confidence in learning that the part would require singing and would later describe the experience as a tremendously enjoyable one.

[88] As promotions for Last Fantasy and its main single "You & I" continued into 2012 in South Korea, IU began preparations for her debut in Japan by playing two shows at the Bunkamura Orchard Hall in Shibuya, Tokyo to an audience of about 4,000 people on January 24, 2012.

[97] Due to her commitments towards preparing for her first solo tour, IU was unable to make broadcast promotions for her fifth Korean extended play, Spring of a Twenty Year Old, which was released on May 11, 2012.

Nearing the end of her Real Fantasy tour and promotions in Japan, IU resumed her hosting duties on Inkigayo after taking a three-month leave due to concert commitments.

[111][112][113] As the series progressed, IU's performance garnered positive critical reviews despite early reservations shown about her casting, with the viewership ratings reaching a peak of 30.8%.

[138] Three tracks debuted in the top ten of the Gaon Digital Chart on the week of release, with the main single, "My Old Story" (나의 옛날 이야기), ultimately peaking at number 2.

[145] Two months after her solo concerts ended, IU made her debut performance in the United States at the KCON music festival held in Los Angeles on August 9–10.

[146] In their review, Los Angeles Times opined that IU had a "sprightly stage presence, and as a solo female singer, she's breaking the molds for K-pop stardom.

[80][6] Despite positive critical reviews and success in the music charts, the album became controversial due to the lyrics of "Zezé" and the audio samples used in the bonus track "Twenty Three" (not to be confused with the similarly titled lead single).

[223] She portrayed different characters in each of the four short films which were written and directed by the critically acclaimed directors Lee Kyoung-mi, Yim Pil-sung, Jeon Go-woon and Kim Jong-kwan.

[239] As the song's title derives from the last digit of the Korean age "twenty-eight" of both artists,[240] it follows IU's previous singles "Twenty-Three" (2015) and "Palette" (2017) which together comprise her "coming-of-age" series.

[252] The following month, IU starred in the film Broker, playing single mother So-young, who initially decides to leave her newborn at a baby box but later changes her mind and tries to retrieve her child.

[14] On April 4, 2023, Big Hit Music announced the second collaboration between IU and BTS member Suga, under his moniker Agust D, for the song titled "People Pt.

[263] IU is set to star as Ae-soon in screenwriter Lim Sang-choon's upcoming television series When Life Gives You Tangerines opposite Park Bo-gum.

The first two songs for which she received songwriting credit were Yoo Seung-ho's "Believe in Love", which she featured on, for the compilation album Road for Hope,[266] and "Alone in the Room" from her third extended play (EP) Real.

[275] IU has also written and performed multiple songs for various South Korean films and dramas, including The Producers,[276] My Mister,[277] Bel Ami[278] and Hotel Del Luna.

In 2022, she was recipient of the Visionary Award, instituted by CJ ENM, which recognizes talents from the Korean film and television industry for their contributions to "leading trends and spearheading innovations.

"[290] In December 2024, IU provided prepaid meals and snacks to people participating in protests, calling for the impeachment of South Korean president Yoon Suk Yeol, following his declaration of martial law.

[297] She has been a regular donor since 2018,[298] helping to support tuition for prospective college students among low-income families, single parents, disabled children, and grandparents raising their grandchildren.

[299][300][301] She makes regular donations on her birthday, debut anniversary and special occasions to foundations helping not only children, but marginalized groups in society such as unwed mothers, elderly people, cancer patients and the homeless, both under her name and her fandom's.

[319] When developer Ntreev Soft had chosen IU to endorse MMORPG Alicia: The Story of My Horse and I, they cited her "simple and innocent" image had complemented with the game's vibe,[319] and featured her in the soundtrack.

[330] IU has modeled for clothing brands Unionbay[331] and Le Coq Sportif from 2011,[332] the SK Planet online store 11st,[333] G by GUESS with Yoo Seung-ho,[334] Elite with Infinite,[335] SBENU with Song Jae-rim,[336] and J.Estina jewelry.

[355] Other endorsements include S-Oil,[356] Homeplus,[357] Nongshim's products,[c] fast-food chain Mexicana Chicken,[360] and Jeju Samdasoo[361] and Binggrae Banana Flavored Milk both in mid-2020.