It looks really nice. I love the variety of values and the textures (examples: tree and grass). Plus, it looks so cute. I'd fangirl spaz over this, but I want to keep this critique as... "nice-looking" as possible. I'm bad enough with these kinds of things as it is.

Okay... how to start. The building...?

The perspective seems slightly off. Because of how the left-most side building is drawn, it looks as though we are viewing this picture from a higher angle than the angle we are viewing Akaito at. Or, if the intention was to view it at a lower angle (same as Akaito's) then the line on the building should be less steep to show that the viewer is more level to the ground. (Try using perspective lines?)

Define the horizon line and the vanishing point more clearly, the faraway grass seems to end abruptly. I think there should be a little more showing since (no matter which angle you choose to stick with) there should be more of the background showing since the viewer is looking down at it. And/or, if looking at it from the lower angle (Akaito's angle), as said before, the building's ground line on the side is a little steep.

Another nice addiction could be slight details. No matter the season, trees will always have leaves on the ground around them (of course, there will be more in the fall). Maybe a random leaf or two might add to it more. Add in a few other types of small plants (weeds, small flowers, clovers?) to add variety..? Also, since Akaito is sitting under the tree, maybe have it cast a shadow over him (with bits of light coming through the leaves?)?

There could be more variety in grass direction (and size) as well, since grass doesn't only just grow in one. Of course, if there is a breeze, then grass will be angle more in the same direction as the wind... If that's the case, then it looks as though the wind is blowing from right to left? Maybe having this breeze show on Akaito more may make it show up more.

And umm... there definitely could be a couple highlights here and there...? Ahh I'm so bad at this. Anyway, I hope this helps a little bit. I'm no expert with backgrounds, perspective, plants... etc.

I sound like I'm rambling... but the main area to focus attention is perspective! _{^{*shot for being bossy, even though it was unintentional*}}

But still, I love this, don't get me wrong! xD