this kid is crushing HARD at this point.
I like how you can never tell how much of nee's teasing is her being a troll and how much is her underlying affections. Since we've rarely seen her side of the story (last ch. was the first time, i think?), her true intentions are still as much a mistery to us as they are to our little boy.
What i also like about this particular manga is how their relationship is pretty balanced. Most stories like this either go for an ultra-motherly girl and a fragile, useless boy, or take the opposite direction and go for an independent, reliable boy and a childish, useless older girl.
While these characters don't match 100% into any category, they still complement each other, which gives them a more distinct personality, imo.