The Arcobaleno ("rainbow" in Italian) is a group made up of the seven strongest infants, who each possess a pacifier that represent the different colours of the rainbow as well with each color corresponding with their Dying Will Flame. Their pacifiers will glow when a member is near another Arcobaleno. The Arcobaleno were transformed from adults into their infant and current forms; in Lal's flashback of the day it is revealed that they were all turned into babies and all seven of the Arcobaleno are shown at least once in their adult forms (Colonnello is not part of the original seven). Each of them has their unique own "curse" and specific abilities, as well as the ability to emit the Dying Will Flame throughout their entire body. They are mentioned to have sacrificed themselves in order to protect the Tri-Ni-Sette (7³), or "ultimate power".
During the 11th Generation, there are now new Arcobaleno which replaced the old ones, which probably died by now.