Vol.5: Can thirteen be… His lucky number?! Wataru tries hard to be a good big brother, which means spending a lot of quality time with thirteen younger sisters! He’s found that his sisters have a lot to teach him, and Haruka shows him that a girl who knows martial arts can come in very handy! From Shirayuki, Wataru learns that people don’t just need nutrition for their bodies, they also need nutrition for their hearts!