Tsukihiro Ren, an ordinary university student, suddenly found himself reincarnated in another world. There, he met his cute little sister, Lilia Silfeed.

A mysterious power identifies her as his "sister," and as she grows, so does he. As he tirelessly strives for his sister's smile, he gradually approaches becoming the strongest being.

But why is this power so fixated on his sister's growth? A major secret that would shake this other world lay dormant—

To become the strongest being, he has no choice but to raise his sister!

Also published concurrently on Kakuyomu!!!