If you liked the Aphorism manga, the Anime-Planet community thinks you'd like:
Over a century ago, mankind was devoured by giant beings of unknown intelligence and origin known as Titans – creatures that eat humans alive indiscriminately and for no apparent reason. The remaining population has managed to survive the last hundred years only by building a multi-walled city capable of keeping the Titans at bay, training military recruits to patrol the perimeter and gather intelligence about their mysterious foe. Eren and Mikasa have lived a relatively peaceful life behind the city's walls, but when a massive Titan appears, smashing the outer barrier and unleashing a wave of terror, their lives are brutally changed forever...
While different in overall plot, both involve a group of people who are brutally devoured by monsters, with similar pacing and terror-filled moments. These are great recommendations for each other.
Both are survival stories with some mystery to them. Aphorism is a little more humorous and the characters feel younger, the story more commercial, but it's still a good category match for Attack on Titan, which feels more epic, desperate, and thought provoking. I found Attack on Titan more original and enthralling, but I enjoyed Aphorism quite a lot as well.
When Ryouga was a boy, he was the sole survivor of a terrible plane crash; with horror, he watched as the other survivors were eaten by a terrifying monster, healing Ryouga's wounds in the process. As a teenager, Ryouga is haunted by these memories and agrees to go with a stranger to a mysterious school for special people. However, little did Ryouga know that within the school's walls lied a brutal game in which cards are used to summon monsters and obliterate other players. Armed with an exceptionally powerful card known as Death Rex, Ryouga must do everything in his power to win so that he may discover the truth behind his past and accept what fate requires of him to do.
Both involve a group of people who get involved in something way more dark than they imagined - though in Chaosic Rune, that period only lasts for awhile and then shifts to something different. Both are super gory and page turners.
Take youngsters, add 30 gallons of blood, a scoop of magical powers, a bucketful of monsters and something that'll mess with their heads most heinously. Stir and bake with thrills and spice it up with action. Let it cool with intrigue and life-or-death situations and serve.