Female protagonist Lin Shuang encounters a weasel while going up the mountain. Upon first meeting, she mistakenly thinks the other party has come to ask for a sealing; the human and the beast engage in witty banter. Under their day-and-night companionship, the truth slowly unfolds—the weasel is not asking for a sealing, but is here specifically to repay a kindness. Years ago when Lin Shuang was young, she had stepped in to save it, and it made a promise to use its lifetime to guard its benefactor. The weasel accompanies Lin Shuang in doing good and helping others, bit by bit accumulating goodwill. When merit is complete, Lin Shuang chooses to let go, fulfilling it and allowing it to return to the mountains and fields. A single thought of kindness arises, echoing across the years. Sticking to one's original heart and doing many good deeds is the best cultivation.