>>283220736
>>283222374
>>283221950
The man you want to thank is Koichi Kikuta. He's the character designer for the anime and a Chief Animation Director throughout the series (the odd numbered episodes in S1, 1/4/8/10 in S2, the movie, 1/3/6/9/11 in S3).

https://wavemotioncannon.com/2017/02/07/konosuba-interview-with-koichi-kikuta-anime-style-009-july-2016/
>Darkness’s proportions also look completely different than they do in the other episodes, don’t they?
>Kikuta: Oh, they do? (laughs) Are you talking about her chest size?
>The size and the way they hang.
>Kikuta: I might have overdone it a bit there. When I was drawing her, I lost restraint. I had the feeling that her breasts were getting bigger—and what do you know? They were slowly but surely getting bigger. (laughs)
>And yet her breasts droop according to the laws of gravity in a realistic way. Were you trying to make that realistic?
>Kikuta: That has less to do with realism and more to do with me drawing whatever I like.
>It doesn’t particularly follow the designs, huh?
>Kikuta: Not at all. Even I thought that they were off.
>(laughs)
>Kikuta: I thought that her breasts were too big and that they don’t droop that low. I might have gone a bit overboard with the whole braless thing. My senses were numb at the time, and when I look at it now, I do think I overdid it. The same thing applies to the boob jiggles. Once I started putting them in, it felt like something was missing when they weren’t there.