Period Cube places you in the role of a girl who, together with her childhood friend Hiroya, starts playing the online game Arcadia in order to search for her missing brother. Commissioned by Mitsu.
While bathing by a spring in the forest, Libera finds you among the bushes, unconscious and covered in wounds. Thinking that keeping you with him will make him more popular among male players, he treats your wounds and decides to take you to Twilight Capital, where he invites you to shop for new equipments. Somehow managing to get away from the players who are after you, Libera runs into some male acquaintances as he takes you to walk around town. Seeing how he’s taking advantage of your presence to get rare items from others, you decide to reprimand him. Unfortunately, Libera is angered by your words and ends up taking you into a forest filled with monsters.