MONGOL800 marks 28 years since forming the band and continues to share music nationwide from Okinawa! "etc.works" is a collection of external works compiling tribute participation songs, collaboration tracks, self-covers of songs provided to other artists, and previously unreleased album tracks realized through connections with artists they have worked with. Following "etc.works" in 2008, "etc.works2" in 2011, and "etc.works3" in 2021, this is the fourth installment in the series, "etc.works4." This work includes a self-cover of "SOUTH WEST BEACH!!" provided to WEST., and "Itsumademo Kimi wo" provided to Yuzo Kazama's 60th anniversary album "DEDICATED to KAYAMA YUZO," as well as covers of famous songs such as Namie Amuro's "TRY ME - Watashi wo Shinjite -," Yosui Inoue's "Shonen Jidai," and Hi-STANDARD's "NEW LIFE." It also includes participation tracks for tribute albums such as Salyu's "Kaze ni Noru Fune" and Dragon Ash's "Tsunagari SUNSET," along with the well-known CM song Hibari Misora's "Kawa no Nagare no Yoni," for a total of 10 tracks. A variety of songs infused with the Mongol800 style results in a work that becomes more enjoyable the more you listen!!