Shingeki no Kyojin: The Final Season - Kanketsu-hen

These are the finales of their respective shows which are considered to be cult classics amongst the Anime community. (Unironically, was also split into 2 parts). Both are a culmination of stories about humanity's struggles of survival & tragedies in a world driven by power balances and doctrinated politics & ideologies. Mutual enemies are established in their respective worlds; due to a convuluted history with implicit narratives that become the catalyst for many countries to wage battles & war; whether by opposing nations or a common 'enemy'. Genocide and an Apocalyptic-Cataclysm occurs under the hands of protagonists whom suffer from the realities of the world built from the aforementioned catalysts. As a result, many characters you have grown to love, meet their end; yet leaving behind their mark in their profound way that audiences will remember for a long time. The stories end with a divisive result that will sure to haunt audiences.  read more 

Both are Shonen/Seinen series with incredibly rich writing, world-building and story-telling. They are modern classics and I would argue that they are both top 3 anime of all time. Everything, down to the smallest details, is connected/explained by these shows and they do not fail to deliver. The music, animation and art style are also really good. Must watches in my opinion. 

Similar surrealism for horrorific/emotionless super strong beings that mindlessly kill those in its way with other certain evolution and some of its creatures being on the more intelligent spectrum to kill. Taking place in alternate horrific worlds filled with isolation and terror from this solid and terrible creatures. Brutality, lots of violence and excessive gore in both titles. 

The ending to both feel bittersweet and memorable in their own regard. Without spoiling, both main characters have a similar turn in ideologies that leads them down a path