Rem's height is 154cm. Why does it look so high in the animation?

This is actually a kind of image processing.

For example, many anime characters have a bunch of hair in the middle of their faces, which is not only symmetrical, but also used to dilute the imbalance of facial distribution (this is generally to make their foreheads look smaller).

Don't say anime. In reality, photography often makes a person's height look different from his actual height through lens processing (you can look at many old photos and check the actual height of historical figures, and you will find many slots)

Finally, Ram must first meet the requirements on the screen, and then compare with others, such as the height difference between Chang and Ram. Similarly, in many cases, the height difference is not always reasonable for the sake of picture coordination (for example, in "Dragon and Tiger", the height difference between them seems to be similar to that between Chang and Ram ...).