Whoa, this is... I love the sun-lit window in the background. <3 How the rays enter into the building and shine brightly onto the pairing, especially the lighting in Natsuki's hair. And then there's the detail put into the two characters themselves; the shading here is fantastic and the colors are vibrant (noticeably on the clothes)!
I love this whole piece! Any more works like this and I'll be obligated to put you on my watch list. <3