KUE-B (Cube) is a behavioral change app that visualizes energy-saving actions in daily life and encourages users to become more aware and make better choices, aiming to firmly establish energy-saving behaviors. The app allows users to record daily actions and spaces as photos and review them in a list or story format. By sharing not only their own past actions but also those of others, users can inspire each other and raise awareness of energy conservation. The activity record is not managed unilaterally, but is designed to emphasize fun and continuity. The simple and calming UI, based on black and green, blends naturally into daily life and allows for easy continued use. KUE-B's goal is for users to be convinced of and choose energy-saving actions themselves. Each small action adds up to big changes. KUE-B supports users in taking the first step toward such a future.