Hello, and thank you for giving DK&S a chance!
I just want to quickly advise you against reading the original story, Couple That Can't Touch.
Diaries of Kōji & Suzuka is more of a reimagining than a rewrite. As eager as you might be to get ahead in the story, reading the original will only lead to confusion—not to mention the potential spoilers.
In the note of spoilers, don't worry much about them. Even though the plot is practically the same, there are many, many differences. The most you can expect is the same situations but executed differently.
If you've read CTCT, it'll take you a bit to get used to the changes. Please try your best!
That was all I wanted to mention. Thanks for stopping by, and I hope you enjoy DK&S 😊