In February 2017, BTS released the repackaged edition of Wings (2016) entitled You Never Walk Alone. Pre-orders of the repackage reached over 700,000 copies, breaking the record for most albums sold in a month. The repackage included an additional four tracks that offered consolation and encouragement to its listeners. Its lead single, "Spring Day" (Korean: 봄날; Romanized: Bomnal) met critical praise as "an intelligent, compelling and elegantly restrained study of loss and longing" that "deliberately avoids cliché pomp and drama" by Dazed Digital. Embodying nostalgia and sorrow, it opened a new chapter in BTS' aesthetics and lyricism and attracted fans across generational boundaries. Upon release, "Spring Day" topped eight of the major South Korean online music charts, as well as Gaon, and crashed Melon's digital chart due to the high influx of user traffic. It also entered the U.S. Billboard's Bubbling Under Hot 100 singles chart at number 15 with "zero promotions." As evidence of its staying power, "Spring Day" is the longest-charting song on Melon by an idol group to date. "Spring Day" later won Best Song of the Year at the 9th Melon music Awards.
In conjunction with the release of You Never Walk Alone, BTS commenced their second world tour, 2017 BTS Live Trilogy Episode III: The Wings Tour, from February to December. The tour visited 12 countries including Brazil, Australia, Japan, Hong Kong, and the United States and gathered 550,000 fans.On the tour, BTS began to play progressively larger venues, moving from halls into arenas and domes. Tickets for the North American leg sold out within minutes and two additional shows were added due to high demand, making BTS the first K-pop act to sell out arenas in the United States. After completing their North American leg, BTS attended the 24th Billboard Music Awards in May and won Top Social Artist, becoming the first Korean group awarded a Billboard Music Award.
Celebrating Korean music icon Seo Taiji's 25th anniversary as a part of his anniversary project "Time: Traveler", BTS released a remake of Seo Taiji's 1995 classic "Come Back Home" in July 2017, reworking the sound and lyrics to similar sentiments toward societal change that Seo Taiji argued for in his songs. BTS was later invited by Seo Taiji to perform as backup vocalists and dancers for eight songs in his Seoul Olympic Stadium concert held early September. During the concert, Seo Taiji acknowledged BTS' thematic similarities to his music and recognized the group as his musical successors, declaring, "This is your generation now. Show them."
Following the depiction of growth and temptation in Wings (2016) and consolation in You Never Walk Alone (2017), BTS embarked on their "Love Yourself" series which sought the enlightenment of self-love through the "起承転結" (Korean: 기승전결; RR: Giseungjeongyeol) narrative sequence of "beginning, development, turn, and conclusion."In September 2017, BTS released the first part of the series, their fifth EP, Love Yourself: Her and featured music from The Chainsmokers' Andrew Taggart for the track "Best of Me". The EP was supported by two singles: the lead single "DNA" and a Steve Aoki remix of their song "Mic Drop" featuring American rapper Desiigner. In the narrative sequence, the EP represented the "承," or "development" of the series and is considered by RM to be one of the major turning points in BTS' career. Within the larger narrative, Love Yourself: Her described the joy and happiness of falling in love. Sonically, the EP served as "a dual exploration of the group's electro-pop and hip-hop leanings," with the first half consisting of "dance tracks that emphasize the group's vocals" while in the second half "the act's hip-hop side arrives in earnest...delivering powerful rap performances."
Commercially, BTS continued to hit new career heights with the Love Yourself: Her EP, debuting at number seven on the Billboard 200 with 31,000 album-equivalent units. In Korea, the EP sold over 1.2 million copies on the Gaon Album Chart in its first month, achieving the highest monthly album sales in the chart's history and the highest on any Korean chart in 16 years, second to g.o.d's Chapter 4 album in 2001. The single "DNA" was released simultaneously with the EP and debuted at number two in Korea. Its music video broke the previous record for most viewed K-pop group music video within the first 24 hours with more than 20 million views on YouTube. "DNA" also became the group's first entry on the Billboard Hot 100 at number 85, making BTS the first K-pop boy band to do so and the second Korean act with a Korean-language song. The following week, "DNA" rose to number 67 and became the highest-charting song on the Billboard Hot 100 for a K-pop group, beating Wonder Girls' previous record at number 76. The following single "Mic Drop (Remix)" peaked at number 28 on the Billboard Hot 100, becoming the first top 40 entry for a K-pop group on the chart. Both "Mic Drop Remix" and "DNA" were later certified Gold by the Recording Industry Association of America (RIAA) making BTS the first and only Korean artist to receive two certifications. "Mic Drop" went on to receive Platinum certification in November 2018, making BTS the first Korean group with a Platinum-certified single in the United States. In December 2017, "DNA" and "Mic Drop" were released as a triple-A side single in Japan with the new song "Crystal Snow", which topped the Oricon Chart and became the highest-selling single from a K-pop artist within a week. The single sold more than 380,000 copies by the end of the year and BTS became the only foreign artist to have a single certified double platinum by the RIAJ that year.
In November 2017, BTS became the first K-pop group to perform at the American Music Awards, raising their profile internationally. That same month, Guinness World Record revealed that BTS had earned a spot in their 2018 edition for "having the world's most Twitter engagements for a music group". In December, they also became the first K-pop group to perform on Dick Clark's New Year's Rockin' Eve to welcome the new year and made their Japanese TV music show debut on TV Asahi's Japan Music Station Super Live. At the end of the year, BTS won their second Artist of the Year at the 19th Mnet Asian Music Awards, becoming the first act to win the award two years in a row. They also became the first artist outside of the "Big Three" to win major awards at the Golden Disc Awards and the Seoul Music Awards, respectively.