After spending their first New Year's together, Yuuta and Saki grow even closer. February brings Valentine's Day and a school trip to Singapore, and in turn, new encounters and realizations. And yet, despite these special events, the pair must maintain a certain distance in order to keep their secret, and so they feel lonely even when together. What will happen when the stepsiblings, who have always held themselves in check, begin to explore a new, more selfish kind of happiness?