A Doppelganger, also known as Shadow, is a crucial part of Summer Time Rendering’s story, so to avoid any major spoilers, this section will only talk about what it is and its impact on the overall story, and not the true nature of the shadow itself nor how it came to be or where it came from.

A Doppelganger in Summer Time Rendering is the same as the meaning of the word itself, which is basically a being that looks exactly like a real person. However, unlike the usual concept of a Doppelganger in most fiction, the shadows in Summer Time Rendering not only look like the real person, but it also talks like the real person, behaves like the real person, and even have the memories of the real person.

The Shadow that appears in Summer Time Rendering is basically a total copy of a real-life person. While this fact alone is already quite puzzling, there are two other things that make the shadows so much more dangerous than other types of doppelgangers that you might’ve seen in other media. The first one is the fact that shadows are aggressive beings. Since they are identical to the real ones in every way, shape, or form, they decided that there’s really no need for the real person to exist anymore. After all, who needs two identical versions of the same thing, right? So the shadows will actively hunt the real humans, kill them, and replace them.

This brings us to the second terrifying thing about the shadows. Regular people wouldn’t be able to differentiate between a real person and a shadow. As mentioned before, they talk, behave, and will perfectly recall the memories of the real one. This means if you want to survive, you’d have to be a total skeptic who won’t trust anybody, not even your parents or significant other. This also means facing a situation where you would have to kill your loved ones because there’s a high chance that they are a shadow, even if every fiber in your being forbids you to do so. It will require you to be 100% sure with your deduction because a slight mistake would mean you would take the life of your significant other. And that is a terrifying decision to make.

Shadows are not the first Doppelganger in anime. There are other series that have used this concept before. It might not be as central to the story as the ones from Summer Time Rendering, but it is still based on a similar concept.

One of the most popular ones is Himiko Toga from My Hero Academia. She can mimic other people’s appearance, right down to their voices. She has used this ability on multiple occasions to either infiltrate the enemy’s rank or to confuse them during a fight. She could also copy their ability, albeit temporarily, later on in the series, which makes her so much more dangerous than before.

For the good people’s camp, there is also Rimuru Tempest from That Time I Got Reincarnated As A Slime and Fushi from To Your Eternity. Rimuru is originally a slime, so one of his basic abilities is copying the appearance of anything or anybody. But that is pretty much the extent of his ability.

As for Fushi, he doesn’t really have an original form, but he can perfectly transform into anything that he feels a strong emotional connection to. Not only that, but he can also fully transform into the body of a person who has passed away and assume their physical ability. However, none of them has the ability to perfectly copy the original’s mannerisms, much less their memories.

The idea of not knowing whether or not somebody in front of you is an enemy or ally, or not knowing whether something is real or not, is not exclusive to the doppelganger. There are also other concepts that are somewhat similar to it but executed in a different way. Two of the most iconic ones are Ghost in The Shell and Naruto.

In Ghost in The Shell, the overwhelming majority of the human population has a cybernetic brain. This means there are people out there who have the ability to hack into those brains and mess with both the memories and the senses. This is pretty much what the antagonist of the first Ghost In The Shell movie did when he hacked into the brain of a truck driver and made him believe that he has a fictional family, and then proceeded to make him see things that do not exist.

Meanwhile, in Naruto, there is a concept of Genjutsu, which is a form of an illusion technique. The Uchiha clan is the master of this technique. They can bind you with their genjutsu and make you experience multiple forms of death in a matter of seconds. Interestingly, the evil plan of the main villain of the series, Uchiha Madara, is basically a supercharged version of this technique. The guy wanted to put everybody in a deep slumber and have them live their best life in the dream world, sort of like the Matrix.