Chihiro, a mother, and her son, Tetsuya, have lived bravely together since losing their husbands at an early age. Tetsuya vows to "protect his mother" in place of his late father, but before he knows it, his feelings have turned into forbidden love... One day, he decides to go on a trip with Chihiro. He is Kokoro to be able to spend time alone with his beloved Chihiro, but is shocked when she introduces him to her boyfriend, Toru, on the trip. Tetsuya just can't bring himself to be honest with Toru, who behaves like a gentleman. One day, he witnesses Chihiro getting entangled with Toru...