Gekka no Himekoi

Rin Nagumo, an intelligence agent for the Karasu Kingdom, infiltrates the Minase household, head of the enemy nation of Ameyane, to gather information. There, he meets Shizuku, a young girl suffering from a serious illness with little time left to live. While initially irritated and envious of her, a stark contrast to his own life spent dirtying his hands for his missions, he gradually finds himself drawn to the warmth she shows him and her determination to live life to the fullest.

(Source: Overlap, translated)