Hoshi no Koe, Saishuu Heiki Kanojo Recommendations
Both a very sad and angsty story about two unappreciated loves, in times of war. In both anime, there are lots of science-fiction elements and the significant other of the protagonist is used as a weapon. Very similiar.
Depressing theme's in both. Each surrounds the life of a couple, and the worry and loneliness each feels.
It really made me think of Saikano when I watched. How two lovers have to be apart because one of them is now "a weapon". And I guess the girl look a little like Chise.