Ushinawareta Mirai wo Motomete: Ushinawareta Natsuyasumi wo Motomete  

Ushinawareta Mirai wo Motomete Special, Ushinawareta Mirai wo Motomete Episode 13, In Search of the Lost Future Special, 失われた未来を求めて　第十三話「失われた夏休みを求めて」

After waking up, Yui realizes it's July 13th, which is new for her. Despite being unsure of what to do, she decides to spend her summer with the Astronomy Club at Nagisa Hanamiya's family villa. The villa has a history dating back to Nagisa's great-grandmother who worked at a nearby military manufacturing plant where she developed technology. While at the beach with the club, a sudden storm interrupts their plans. They take shelter at an abandoned factory nearby, which eventually leads them to discover a hidden underground bunker. What they find in there might shed light on a previously unknown future connection.

Ushinawareta Mirai wo Motomete: Ushinawareta Natsuyasumi wo Motomete was given as a bonus Blu-ray disc to customers who purchased all six Blu-ray volumes of Ushinawareta Mirai wo Motomete.