TVXQ released their sixteenth Japanese single, "Purple Line", on January 16, 2008. It debuted atop the Oricon, becoming the group's first number-one in Japan and making them the first foreign male group to have a number-one single in Japan. They then released their third Japanese album, T, which debuted at #4 on the Oricon Weekly album chart. TVXQ's label Rhythm Zone, announced the "Trick" project where five singles would be released consecutively for six weeks, from February to March and each single would contain a solo track by a member. The group released their twenty-second single, "Beautiful You / Sennen Koi Uta" in April. The single became another number-one for the group and made them the first non-Japanese Asians with two number-one singles since Ou-Yang Fei Fei set the record 24 years before. They returned to Korea to participate in the 14th Annual Dream Concert at the Olympic Stadium in Seoul on June 7. On June 12, TVXQ concluded their Asia Tour in Beijing which had begun on February 23, 2007 in Seoul. TVXQ returned to Japan and released their twenty-third single, "Dōshite Kimi o Suki ni Natte Shimattandarō?" The single topped the chart, making TVXQ the first foreign artists to have three number-one singles on the Oricon. They performed at Avex's 20th anniversary meeting and at A-Nation '08. In August, TVXQ returned to Korea once again to take part in SMTown Live '08. They performed alongside label-mates BoA, Cheon Sang Ji Hee the Grace, Zhang Liyin, Girls' Generation, SHINee and Super Junior.

The group's fourth Korean album, Mirotic, was slated to be released on September 24 but due to the large number of pre-orders was pushed back two days. Like their previous Korean album, Mirotic debuted atop the charts with 307,974 copies sold. In early January 2009, the album's sales totaled 502,837 copies, making it the first Korean album in six years to pass the 500,000 mark. In October, TVXQ released "Jumon: Mirotic", the Japanese version of Mirotic's title track. The single topped the Oricon chart, breaking the record that the group had set with their previous single. TVXQ attended Kōhaku Uta Gassen Music Festival on New Year's Eve, making them the first Korean group to attend.

Their twenty-fifth single "Bolero/Kiss the Baby Sky/Wasurenaide", released in January 2009, became another number-one for the group. In March, TVXQ released their twenty-sixth single "Survivor" which debuted at #3 on the charts subsequently ending their number-one streak. "Survivor" was followed by their fourth Japanese album, The Secret Code, which debuted at #2 on the charts. To support the album they embarked on their fourth concert tour, Tohoshinki 4th Live Tour 2009: The Secret Code, which ended at the Tokyo Dome, making them the first Korean group to perform there.

On April 22, 2009, they released their twenty-seventh single "Share the World/We Are!". The single debuted atop the charts, extending their Oricon record.[63] Their twenty-eighth single, "Stand by U", was released on July 1, 2009 and debuted at #2 on the charts.

The group's live DVD titled "4th Live Tour 2009 - The Secret Code - Final in Tokyo Dome" was released on September 30. According to the 10/12 Oricon DVD Ranking, it sold more than 171,000 copies, their personal best for sales in this category. In addition, this is the first time in twenty years for a non-Japanese Asian artist to get first place in the DVD rankings, exceeding previous foreign artists who have attained this ranking included The Beatles' "The Beatles Anthology (Special Price Edition Edition)" which was released in March 2003 and Led Zeppelin's "Led Zeppelin DVD", which was released in June 2003 and have held that position for foreign artist getting first for 6 years and 3 months since. Also, based on the sale numbers of their DVD, they broke their personal record by pre-selling 107,000 copies. Their previous records include their 3rd Live Tour 2008 - T which was released in August 2008 and was last recorded as having sold 112,000 copies, and All About DBSK Season 3 which sold 66,000 copies so far. This time, their DVD sold more than twice that amount with a total sales of 171,000 copies and broke the record for the highest initial sales for foreign artists.