In the lead up to their next album, BTS released an original eight-episode documentary series exclusively on YouTube Premium entitled Burn the Stage that ran from March until May 2018, offering a behind-the-scenes look at the group's 2017 Wings Tour. In April, the group also released their third Japanese studio album, Face Yourself, which debuted at number 43 on the Billboard 200 as the third-highest-charting Japanese album in the history of the chart. In conjunction with the release of Face Yourself, the group released a nine-minute short film titled "Euphoria: Theme of Love Yourself: Wonder," which featured the song "Euphoria" and embodied the "起" or "beginning" of the narrative sequence.
In May 2018, BTS released their third Korean-language studio album, Love Yourself: Tear in conjunction with an appearance at the 25th Billboard Music Awards. At the show, BTS debuted as performers with the premiere of their lead single, "Fake Love" and won Top Social Artist, making them the only Korean artist to win the award two years in a row. In the narrative sequence, the album coincided with the "轉" or "turn" of the series, touching on the tortuous enlightenment of loving without being loved and encouragement to those without dreams. It received generally positive reviews from critics. Caitlin Kelley from Billboard described the album as "one of their most thematically cohesive yet sonically varied albums, with maximalist production erupting against lyrics about emptiness," while Sheldon Pearce of Pitchfork wrote that the album "formula is a slick, loosely thematic album about love and loss, with a stronger focus on rapping than ever before" and that it "aims for cohesion and produces fun, prismatic songs in the process."
Commercially, Love Yourself: Tear was one of BTS' most successful albums, bringing them to new heights both domestically and internationally. The album debuted at number one on the U.S. Billboard 200 with 135,000 album-equivalent units (including 100,000 pure album sales), becoming BTS' highest-charting and first number one album in the US, the first K-pop album to top the U.S. albums chart, and the highest-charting album by an Asian act. Love Yourself: Tear also became BTS' first top ten hit in the United Kingdom, reaching number eight on the UK Albums Chart. Their single "Fake Love" became their first top ten hit at number 10 on the Billboard Hot 100, becoming the seventeenth non-English song to reach the top ten and the first by a Korean group. "Fake Love" later became their third single to attain Gold certification by the RIAA that August. In South Korea, Love Yourself: Tear sold over 1.6 million copies in its first two weeks, making it the highest monthly sales for an album since the Gaon Chart's inception at that time.
As the conclusion of the Love Yourself series, BTS released their second Korean compilation album Love Yourself: Answer in August 2018, which contained songs from the previous Love Yourself releases along with seven additional new tracks. The album was supported by the lead single "Idol" and the alternative digital release featuring Nicki Minaj. Thematically, Love Yourself: Answer placed the songs of the Love Yourself series within the narrative of beginning, development, turn and conclusion to illustrate the excitement of love, the pains of farewell, and the enlightenment of self-love. Critically, the album received generally positive reviews, with Billboard calling it a "masterful culmination of years of work and rife with meaning" and "undeniably a magnum opus from BTS that that few other artists, boy bands or otherwise, ever can hope to achieve."
Commercially, the record sold over 1.9 million copies on the Gaon Album Chart in August 2018, breaking the chart's all-time monthly record once again. The album became BTS' second number-one album on the U.S. Billboard 200 and their highest sales week in the country at that time, making BTS the only K-pop act with two Billboard 200 toppers and the first pop act with two number one albums in less than a year since One Direction topped the chart with Midnight Memories in 2013 and Four in 2014. Love Yourself: Answer later became the first Korean language album to be certified Gold by the RIAA in November. In Canada, Love Yourself: Answer became the band's first number-one album on the Canadian Albums Chart. In the United States, "Idol" peaked at number 11 on the Billboard Hot 100. The single "Idol" also reached number five on the Canadian Singles Chart, marking BTS' first top-ten hit in Canada. The music video for "Idol" received over 45 million views in its first 24 hours on YouTube, breaking the record previously set by Taylor Swift with "Look What You Made Me Do". "Idol" and Love Yourself: Answer later received platinum certifications, both selling more than one million certified units in the United States. "Idol" became the group's third Platinum single while Answer became the group's first Platinum album, making BTS the first Korean artist to attain this certification in the US.
In conjunction with Love Yourself: Answer's release in August 2018, BTS commenced their third world tour, BTS World Tour: Love Yourself, with a landmark concert in the Seoul Olympic Stadium, the largest stadium in South Korea. During their tour, BTS also featured on Steve Aoki's single "Waste It On Me" released that October, which was their first and only all-English language feature. On tour, BTS continued to play to progressively larger venues from arenas to domes to stadiums. For the final stop of the North American leg, the band performed at Citi Field in Queens, marking the first time a Korean act has performed at a U.S. stadium. All 40,000 tickets for the stadium date sold out in under 20 minutes. According to StubHub BTS was one of 2018's best-selling concerts in international markets outside the US, second to only Ed Sheeran. Vivid Seats named BTS the 2018 artist of the year, citing the group's history-making concert at Citi Field. The tour also received generally positive reviews from critics. Philip Cosores from Uproxx described BTS' four nights at the Staples Center as an "enormous, multi-sensory experience" bringing an "inclusive" and "multicultural experience" where music is above any language barrier, while Crystal Bell from MTV said "BTS have created an experience so captivating, so inclusive, and so visually stunning that it's cemented the boy band as one of the most vital acts in pop music today." That October, with more than a year remaining in their contract, BTS renewed their contract with Big Hit Entertainment through 2026.
In early November 2018, a popular Japanese music show cancelled BTS' performance citing a T-shirt a member wore the year before. In the same month the Jewish human rights organization Simon Wiesenthal Center (SWC) stated BTS owed victims an apology for the shirt in 2017, clothing with Nazi symbolism, and a flag. Big Hit Entertainment issued an apology, saying that the images on the clothing were not intended to be hurtful to the victims of Nazism or atomic bombings, and that the band and management would take steps to prevent future mistakes. They also stated the flags were meant to be a commentary on the Korean school system. The apology was accepted by SWC and the Korean Atomic Bomb Victim Association.
Crossing over to film, BTS released Burn the Stage: The Movie in theaters worldwide in November 2018 to commercial success. In the United States it accumulated $1.2 million on opening day for a total of $3.54 million over the three day weekend, breaking the record for the highest grossing event cinema musical production which was previously set in 2014 by the band One Direction. It ranked at number ten in the box office despite selling at only 620 locations compared to the 2,000-4,000 locations for the other top ten sellers.
At the end of the year, BTS won their third Artist of the Year at the 20th Mnet Asian Music Awards in a row and ranked number eight on Billboard's year-end Top Artist Chart alongside the likes of Drake and Taylor Swift and were also the number two act of the year in the Duo/Group ranking, only behind Imagine Dragons. They also made the Bloomberg 50 due to their "willingness to address social issues, mental health, and politics, despite being in a genre often painted as bubble gum pop". The group sold more than ten millions albums in South Korea alone, with five million being sold in 2018 alone.