Rewrite 2nd Season

These two anime has dark philosophical meaning behind them. Both about destroying civilization. Only difference is one is already destroyed and the other one is the path to salvation.  

The main characters do not resemble each other, but the side characters of the two animes are similar to each other. Most of the side characters are girls, and there are two little and mysterious girls in the two animations. One of the horror moments of fantasy kind is they have deep backgrounds and similar storylines to each other. 

Semi-overpowered main character does things he doesn't want to do to save the world from ruin. Along side him is a loli character who has more of an impact to the story than you might think. Along the way, the protagonist meets different characters that he befriends/betrays. Casshern Sins is more of a psychological anime with slow pacing compared to Rewrite which is more of a fantasy/action anime. If you like one, I am sure you will like the other. 

After you watched episode 5, you will have a feeling that they look similar. - Organization - Interesting storyline - Both MC trained to become a soldier / guardian before they become a professional hitman / killer / spy. 

Main characters in both anime need to make a lot of hard choices and abandon everyone and everything to achieve their goal. While Kotarou's and Kirtsugu's personalities are different, their circumstances and way of saving the world is very similar. Both shows are on darker and more depressing side, while not being tearjerkers. 

If you enjoyed the Sci-fi storyline & painful situations in Steins;Gate, you should also enjoy Rewrite 2nd season (watch Rewrite 1st season is optional).