IS: Infinite Stratos - World Purge-hen

While Ichika Orimura departs to visit Kuramochi Engineering's laboratories, an unidentified enemy hacks into IS Academy's core and cripples its systems. To fend off the attack and repair the damage, his older sister Chifuyu enlists Ichika's harem: Houki Shinonono, Cecilia Alcott, Huang Lingyin, Laura Bodewig, and Charlotte Dunois. Together, they utilize virtual reality to confront their opponents in IS Academy's network.

Unbeknownst to the girls, a piece of malware named "World Purge" is activated when they enter the digital realm. The program forces them into fabricated realities, where they each experience an ideal romantic version of their bond with Ichika. Once Ichika returns to IS Academy, it is up to him to rescue the five girls and wake them from this virtual reality.

(Source: MAL Rewrite)