Kimi wo Ushinaitakunai Boku to, Boku no Shiawase wo Negau Kimi

"I want you to be happy, Sou-chan. But that's why...I'm not good enough." During my first summer of high school, I finally realized how I had felt and confessed my feelings when my beloved childhood friend said these words to me. She told me that she didn’t have much time left, but wouldn’t elaborate. And from that day onward began my trial for the sake of a future that allowed us to be together. (Source: Kadokawa, translated)