The song itself is an interesting mix between the two artists' styles, and they mutually wrote, composed and arranged it. Miyazawa added in the bossa nova and a bit of samba that builds up towards the end, while Yano provided her signature piano riffs. If you're familiar with her jazz-flavored pop material from the 90's, you'll know what I mean.
Seriously, I made the best breakfast in months thanks to this song. Not as good as the stuff they're having in the video, though.