Last year at the start of the US tour, someone got a picture of the setlist.
That’s where fans figured out the name’s “Elevator Girl” and “Tattoo”. Elevator Girl remained, but Tattoo has been changed since then, and is officially “Kagerou”. Fans now found the official title on the recently released The Chosen Seven blu-ray set (Sold out).
The word kagerou itself is in the lyrics of the song. Kagerou can mean many things; heat haze, the mirage, moth, mayfly. It’s also used to symbolise something that’s short lived.
– The Chosen Seven blu-ray set