IDEA: A crossover with Metal Gear Series and Attack on Titans-Shingeki no Kyojin: SNK.
Setting: in the world of SNK where the titans are always out of the wall waiting for a chance to enter and kill humans.
Timeline: Pre-Post or During events of the manga (SNK Manga, Before The Fall Manga/Novel and Levi's Spinoff manga)
Focus: Centers on a Survey Corps member that might have survive previous expeditions out of the wall during the run she/ falls inside a fissure while being chased by titan and ending a broken bone in a undergorund cavern finding no exit the character go further inside the cave as the character goes deeper he/she starting to be aware that something is off about this cave.
Plot: A survival story as how the character tries to get out of the hands of what is left of the facility's security system, while unintentional unravels its mysteries.
MGS Inspiration: The functional Android with individual AI or Cyborg that might support the character survival while it's inside of the facility giving the tips of how to use some tools he/she finds in the way. The fire arms, gadgets, files involving events of Metal Gear series and maybe the intercom with the support.
Atmosphere: taking some elements similar to some Survival Horror games such Bioshock, Outcast, Extermination, Resident Evil 1,2,3,4, Silent Hill, F.E.A.R. series and DOOM series where most of the character try to survive in an alien (unknown) hostile like ambient where everything turns calm and quiet to rush the tension even higher to the peak with maybe some surrealism. While gathering what tip of information they can while keep enduring their bodies and maintaining their will sharp on staying alive.
Tips: If someone takes this idea please whatever you do please try to take in detail the emotional status of the character at the situation at hand. And maybe start with some sort of chronology/diary entry since the survey corps must record every anomaly they see all piece of information they gather during the exploration.
Condition: The character must not be a Titan-shifter or any kind of super human nor character any character only minor or those who died in the actual series or presumed to be dead. Just human with its mind edged by his will to survive another day and its body endured by his hard work and previous experience as a survey corps member. But might it last until he is able to see the light again? The characters of the original series can make cameos since in everyday life you meet people and possibly giving some insight to the background of the character.
Incase: It isn't require to be MGS crossover since it always possible that this might happen in the actual series anyway.
Author Notes: This is an Idea I wanted to share that popped in my mind when I was replaying metal gear solid 4 guns of the patriots and metal gear solid 3 snake eater. I post this with the desire of whispering inspiration and stimulating the one that might take the challenge. And yes my main intention was to mind R Pe with my hard erected idea while penetrating with the strength of a suggestion and cum inside with words and ending with the desire of actually writing the story. So please PM me if felt the idea if not it was too short.