Won't you play with me, nii-san?

Osomatsu and his other three brothers (Karamatsu, Choromatsu, and Ichimatsu) we enjoying their lovely life till the day their mother announced their was another baby on the way. The sweet little Jyushimatsu was born but he has some problems. One he doesn't understand much. Two he has problems walking. Three he knows Ichimatsu doesn't like him one bit. The 19 year old, Osomatsu tries to get Ichimatsu to understand Jyushimatsu is a very special boy but Ichimatsu ignores his older brother. Ichimatsu starts watching Jyushimatsu and starts noticing things he didn't before, like how his little brother loves baseball. Ichimatsu realizes Jyushimatsu may not be able to live forever but he once he realized this, he is to late.