18+ 3Ping Lovers!☆Ippu Nisai no Sekai e Youkoso♪ The Animation

Tomohiro, who is obsessed with medieval history and related games, was summoned by the warriors Alice and Frey into their world. There, Tomohiro has the ability to permanently increase the magical strength of female warriors many times over. In return for this help, Alice and Frey promise to marry him. The transfer of magical powers then takes place to the complete satisfaction of all concerned. Together with the four fierce warriors Lumines, Lolo, Cature and Rachel, Alice, Frey, and Tomohiro attempt to liberate this world.

(Source: Anisearch)