Art of Explosive Hades Fall

Katana World (After a set order is played, put it into the order zone) Play this with [pay a gauge]! :When this card is put into the order zone, search your deck for up to one card, put it into this card's Buddy Soul face down, and shuffle the deck. Order Zone:When your opponent's rear-guard is placed during their main phase, [discard a card from this card's Buddy Soul], if the grade of the card discarded for this cost is the same as that placed unit's grade, retire that unit. (The placed unit's abilities are not nullified)