盟友宣言！
Sworn Friend Declaration! is a Weiß Schwarz card from 転生したらスライムだった件 Vol.3 TSK/S101-040. Compare listings from Singapore Weiß Schwarz sellers on CardJio, then jio them on WhatsApp.
Choose 1 of your characters, and that character gets the following ability until end of turn. "【AUTO】 When this card's battle opponent becomes 【REVERSE】, you may choose 1 《Demon Continent》 character in your waiting room, and return it to your hand." Put this card into your stock.