Ukkari Osananajimi to Kekkon no Yakusoku wo Shiteshimatteta Kekka

Seventeen-year old Ryo jokingly promised to marry his six-year old childhood friend Yuka.
Ten years later, at the age of 16, Yuka still remembers the promise, but Ryo already has an older girlfriend, Kasumi!
This is a slapstick comedy that unfolds as even Kasumi is affected by the innocent and kind Yuka.
How will the three people end up...!

(Source: YouTube, translated)