User blog comment:KodachiZero/Weekly News - 11/@comment-73.211.252.152-20160816203153/@comment-26432452-20160817023529

That's for event forging. 5 copies of that will gives you 100% chance to forge Zarobi's special weapon with extra damage to poisened/slowed enemies ability. A copy only gives you 5% chance so keep it until you have 5 of that.