Sunny

From DrCoke at MangaHelpers:
Against his will, Haru is forced into living with his brother's daughter Akira, who lost both her parents, for three months. He never wanted to come back to the house where his brother and sister-in-law lived, nor did he want to see Akira. All of these reminded him of the bitter memory of love that he's kept sealed away. Now, Haru has to take care of Akira and her two roommates and come to terms with his painful memories.