In 19th century Paris, Claude Claudel and his grandfather Oscar run a metalworking shop tucked away in the Galerie du Roy shopping arcade. Back home from his recent travels, Oscar appears with a young Japanese girl—Yune—by his side. Although he is initially against it, Claude comes to accept Oscar's announcement that Yune will live and work with them going forward. Bewildered by Yune's foreign customs, Claude must balance looking after her and managing the shop. But over time, as she settles into her new role as a live-in maid, Claude slowly shows interest in learning to understand Yune and the vastly different world she comes from.

While searching for a run-away cat the twins Riko and Rimu Mikogami find a strange device that transforms them into Kirumin. It also enables them to turn into real animals. Their older sister Nagisa soon joins them. Now the three have cute, funny and sometimes dangerous adventures.