Toaru Ryoushu no Shuuchakuai no Hate

"You are the savior of this world." The protagonist Maika is summoned to another world by a young lord named Ash. A world where alchemy is a considered a forbidden art. As they spend time together, the two naturally become closer, and eventually start a physical relationship.. but Maika experiences flashbacks of memories she has no recollection of experiencing. While Ash is away, she happens upon a warehouse.. "Have I been here.. before?" and uncovers a hidden underground laboratory where she finds.. Herself. A row of water tanks, with humanoids floating inside.. humanoids who look just like her. From that moment forth, her sweet dreamlike life with the lord.. is shattered.