Hitoribocchi Kami-Sama no Yangotonaki Tawamure
Key look-alike
Monokuro Limit
I didn't see a happy ending, the seme and uke at the end didn't even know one another, they just got together because the other looked like someone they did love. Rue starts the whole "I love you" think on their very first meeting! You can't love someone that fast, you can just love what they look like, especially since Kuro's and Mashiro's personalities are completely different. And vice versa with Rui. They were just substitutes for the ones they used to love. That's it. That's all the end relationship was. You don't see them grow together, you don't see them fall in love, and Rui kept calling the uke by the android's name. The ending never made up for the the sadness of the previous chapters because that "love" was completely hollow and based on trying to make each other fill a role left by someone they look like. You never see them loving each other for who they are. They try to hint at it at the end, but 1-2 pages does not make up for an entire volume of watching them fall in love with someone else. It just feels sad and empty.
Amagami wo Kimi ni