Rule Breaker, a similar weapon from a different series.
Summon Breaker is a knife created by Quattro. It prevents Topaz from summoning, and also nullifies his Mimicry abilities. It looks like an ordinary kitchen knife, though a larger one. It can possibly change its shape to its wielder's liking.
The blade was first introduced in blog Example #202: Knife to meet you!. The weapon was in Brawler/Tae's possession far after Quattro was defeated. It was given to Osaka who then presented it to Topaz. In the same blog Ryouko Asakura took control of it, and continued to wield it until Topaz's death in Example #204.
After that, it was lost for some time. It was next seen in Catnip's possession, after she wished for a weapon capable of defeating Topaz. She gave it to Hikage sometime prior to Example #283, where Hikage used it to defeat Himari as well as Yagyuu's Squid familiar. It is unknown who currently holds Summon Breaker.