Kotonoha no Niwa + Lifelike animation.
Fun fact, the director/writer/editor for Garden of Words is Makoto Shinkai. Probably most famous for 5 Centimeters Per Second. He actually did an OVA length short story called Voices of the Distant Star all by himself, including part of voice acting (his gf provided the female voice) along with two other shorts. Gorgeous work too.