Rurouni Kenshin: Meiji Kenkaku Romantan - Seisou-hen

Just like the Kenshin prequel, both are recommended because of the swordplay, romantic drama, and dark theme. 

Both are historical stories that revolve around main characters dealing with troubles and sad lives. 

Same concept here really. Same sad broken main character after the loss of a loved one. The 2nd girl tries to bring him to her side but ends up getting hurt in the process, although in RK "reflections", the main heroine completely fails, where the main girl in "rumbling hearts" gets a happy ending in the end. You should watch this if you enjoy the pain and realism that people go through in love triangles, and how people deal with the loss of a loved one. These two anime are similar in an abstract way. 

Both have a melanycholy and darkly dramatic feeling.  

both Casshern and kenshin sufer from pinful sin of thy past. both of thy show are sad sequels style of long TV anime . 

Despite having the potential to become one of the best anime in the past decade, they both drown in their ambitions by the petty melodrama and inconsistent characters. These two series are a must watch if you love tear jerkers.