Rational number" is tetote's third single. The album is the third single from tetote, "Rational number", which continues to feature arranger Yoshiki Niioka. The first song "Maboroshi feat. Akira from RiTTLEBOY" is a rearrangement of the previous song "Maboroshi" with Akira, the vocalist of RiTTLEBOY, and is a more poetic song. The song "fools" features drummer Iwasaki Takuma and was the first song recorded with live drums by tetote. It is a standard live song, but it has a different atmosphere from the live performance. The sound of "Immortal" is constructed by Daichi Arakawa using elements of industrial music. The three songs on this album will keep you interested in the music.