Cartouche of Solidarity

This amulet is carved from lapis lazuli with scenes of cooperation, and seems to glow pearl-white from within. While attuned to the cartouche, you gain a +1 bonus to attack rolls made against creatures that have been damaged by an ally since the end of your last turn. In addition, once per long rest you can use your reaction when you become the target of an attack to summon a guardian spirit which defends you, giving you a +1 bonus to AC until the start of your next turn, including against the triggering attack. While attuned to a cartouche, any other cartouches do not count towards the number of items you can attune to. The bonuses granted by this cartouche increase by +1 for every cartouche you are attuned to.