|Abilities||Part of Sistema C.A.I, Ignites Flames|
|Flame||Rain, Sun, Lightning, Cloud|
|Manga Debut||Chapter 191|
The Skull Rings are the Rings of Hayato Gokudera's Sistema C.A.I. and are comprised of Lightning, Rain, Sun, and Cloud attribute rings. None of them were seen until Gokudera's second battle with Gamma. He uses them to open his Sistema C.A.I Boxes, which pack different Flame-property artillery. He can then use that artillery to attack the opponent.
Rain Tube: A regular Storm Flame attack with Rain Flames added. The Rain Flames' Tranquility characteristic makes it easier to break through Flame shields.
Sun Cartridge: A machine gun-like attack. The Flame Arrow uses special bullets that are infused with Storm Flames and sped up by Sun Flames.