And I don't know if they used the same term in Japanese. But the fact that Kou asked Rin to continually "watch" over her. While both Kou and Aoba promised to watch over each other, may indicate that they have a more rounding mutual relationship. A bit far-stretched, but I will take whatever shipping material the author hinted at right now
Kou and Aoba said they'd watch each other, not watch over each other. As in track each other's careers.
Happy, yet sad. The tone, plus the fact there's practically no one else asi of them, makes an interesting atmosphere that goes from isolation to intimacy. I'm afraid of what might come in the third part. Hopefully i'll turn more like Cross Heart finale.