WARNING: The following contains spoilers for Link Click, now streaming on Funimation.
Time travel is a tried and tested trope in storytelling. Recently, there has been a shift in how anime and donghua have been interpreting it, though. In Link Click, which was part of the spring 2021 anime lineup, time travel is done through photography, and its two protagonists, Cheng Xiaoshi and Lu Guang, mainly use it for business, fulfilling various clients' requests -- be it to help solve a crime or a more personal request, such as delivering messages to a loved one. Here's how Link Click's unique use of time travel works.
Link Click's Time-Travel Mechanism, Explained
Cheng Xiaoshi and Lu Guang's time-traveling powers are activated through high-fiving each other. As soon as they do that, Cheng Xiaoshi is sent into the body of a photographer and momentarily takes it over. Not only does he gain control over the person's body, but he also unlocks their emotions. When he's in Emma's body in Episode 1, for instance, her homesickness hits him so hard that he decides to help her by sending her parents a text message. In Episodes 4 and 8, Cheng Xiaoshi experiences each of his respective host's feelings of infatuation when they encounter their crushes.
However, Cheng Xiaoshi doesn't have to use someone else's body when he goes into the photos. The donghua features a few instances where he appears as himself. In Season 1, this only occurs if the photo is taken by a surveillance camera. While this can be convenient in a few ways, Cheng Xiaoshi has to take extra care to not be seen while he's in the photo -- after all, he's not supposed to exist in that particular person's past.
The Rules of Time-Travel In Link Click
Time travel can be a fickle thing, which is why Link Click's duo has three rules they have to adhere to. One is that Lu Guang can only see 12 hours into the future from the time the photo is taken, which means he and his partner only have that specific time frame to finish their cases within. This is due to the limit on Lu Guang's future sight, and it's assumed that Cheng Xiaoshi gets automatically pulled out of the photo once the 12 hours are up. However, this doesn't stop Cheng Xiaoshi from exiting the photo of his own volition.
The second rule is one that Cheng Xiaoshi struggles with at times: listening to Lu Guang and not changing anything when he enters the photo. The third rule is perhaps the most important, though. Do not change the past.
Most of the time, the two -- or at least, Lu Guang -- try not to alter anything when they travel to the past because if it does get changed, it will have a butterfly effect on the future, potentially creating an alternate timeline. The only time when changing the past wouldn't change the future is if death is a factor. If Cheng Xiaoshi tries to save someone who is destined to die, then the future will change.
How Cheng Xiaoshi & Lu Guang's Time-Hopping Partnership Works
Cheng Xiaoshi and Lu Guang work seamlessly as partners throughout Link Click. Lu Guang is the "observer" while Cheng Xiaoshi is the "executor." Lu Guang uses his powers to scope out a case and then tries to see what will happen in 12 hours after the photo is taken. His powers are limited by who took the photo, though -- he can only see what happens from the photographer's movements. If the photo was taken by a surveillance camera, then his field of vision is limited by the camera. It doesn't appear as though the two of them can switch these roles; their powers seem to be set in stone.
Cheng Xiaoshi usually relies on Lu Guang's insights when he enters the photo. Lu Guang will tell him whether the photo is actually useful for them to solve the case and will instruct him on what to say or do. That doesn't mean that Cheng Xiaoshi has to follow what Lu Guang says to a T, though. The problem is that if he does something out of character, it will look suspicious.
At first glance, it looks like Cheng Xiaoshi doesn't have much autonomy since he has to rely on Lu Guang to enter the photos. But there's a loophole: Cheng Xiaoshi can jump into the photos if he high fives himself. The downside is that he loses all contact with Lu Guang and will not be able to communicate with his partner if he does so. Cheng Xiaoshi will not know what happens in the photo either, leaving him considerably vulnerable. We'll have to see if a second season of the donghua adds to or changes any of these unique rules and mechanisms.