They are multiple circles composed by small bone-like parts that expand themselves and float around once charged with Dying Will Flames. The space between the loops is filled with a screen of Storm Flames.
They mainly serve as shields, but can also be used to immobilize enemies by surrounding them like a prison. They can also be simultaneously charged with Flames of other attributes for compound effects, such as having an extra layer of Rain Flames that partially neutralize attacks with their Tranquility characteristic. The Bone Loops are currently part of the Gokudera's Cambio Forma Version Vongola Gear.