Suna no Ue no 1DK

An innocent woman is injured during a sabotage operation at a research institute. On the brink of death, she is somehow healed when cells of unknown origin that were being studied there hijack her body. The life-form, christened "Algernon," slowly acclimates to human life. And what it wishes for is to live a peaceful life, like that of any other human being.

(Source: Kadokawa, translated)