Kai growth as a character is really good, personally, i don't want him to lose part of shyness but i like for him to gain confidence and him having the insight to see the nuances of those girl actions was really well done.
The last page of him in the field was simply epic.
It's interesting to note that he didn't say anything about himself until he confirmed when Kai was from. Why antagonize a potential ally? Literally: while enemies in WWII, Japan and America were allies in WWI.
Again, Shinju no Nectar takes some interesting steps. An American character from the 1940s cheering out loud when our Japanese protagonist tells him that the Allies won WWII? Not something you see every day in manga.
Also, now we have Mongols (excuse me, "Altai") with tanks. This is going to be fun.