I like them because of their compelling relationship, and even just looking at them, you can tell there's a lot of high strung emotions here. The black and blond, the blue and red- Fire and water, young and (not too) old, tall and not so tall.
The fact that Roy has his eyes closed symbolises that he is the assertive one in the relationship, and you can see that Edo is blushing, and has his eyes open, because he isn't so sure about it. He's also kinda awkward that Roiroi has one hand on his crotch. (XD, but he likes it!) The vague figures of the background, assembled and cheering, symbolise their surrounding community in the military, which is loving and supportive of such a compelling gay couple. Yay for them for being so progressive in 1915!
You can see that the sky is blue, clear, completely free of clouds and that symbolises that they are heading for a bright future, with very few relationship problems. (They're probably headed straight for marriage!)
The bird symbolises... well, it's just there coz I like birdies.
Thanks for enjoying!