Art of Explosive Hades Fall

<Katana World> (After a set order is played, put it into the order zone) Play this with [COST][pay a gauge]! [AUTO]: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. [AUTO]Order Zone:When your opponent's rear-guard is placed during their main phase, [COST][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)