Actually, I did enjoy reading this one. It's sweet and cute. I know a lot of people cried and it's often listed as a "tear-jerker", but, I don't know, I wasn't attached enough to any of the characters to cry for them. Butterfly, the main character, was cute, cried often, and was not particularly mature or strong, even at the end when she aged a couple of years. She was bland, boring, plain, and as was her love interest, Chinatsu. He doesn't have any driving characteristics, save for being handsome and patient. But the romantic development between them was nice.
On that note, I think the ordinary atmosphere is actually one of the driving points of the manga. It's set during WW2 war-time, but it shows the ordinary, unaffected lives of regular citizens. I did like the historical information provided, and it was actually mostly accurate. I enjoyed the way that the plot was developed in the beginning, but I vehemently disliked how many turns and cliches that the ending had.
Also I really hated how the author tried to do that cliffhanger with Chinatsu "maybe dying". I think Butterfly would have been way more mature if he had actually died, but whatever.
Also, I usually am not a fan of age gaps, and I will admit that it bothered me in the beginning quite a bit.
TL;DR: Cute, nicely-developed, but would have been much better executed if the mangaka steered clear of unrealistic cliches. Therefore, 7/10.