https://graphql.org/

Eg. Monika ones can be get on:
https://doki-doki-literature-club.fandom.com/wiki/Monika_(DDLC)/Sprites

Make this works in the browser (This working from Deno/Node.js).

fetch('https://ddlcapi.herokuapp.com')
.then(response => response.json())
.then(console.log)

Hi there! Very interesting project, and I've looked through some things.

There are a few things that I find quite confusing and an odd choice to add, so I've added some things I believe you could change to improve this API.

First, on the characters.
The JSON returned is
{ "name": "monika", "age": 18, "born_date": "September 22nd", "concept_height": "160 cm", "gender": "Female", "hair_color": "Coral Brown", "eye_color": "Emerald Green", "filename": "monika.chr", "appears": ["Act 1", "Act 2", "Act 3", "Act 4"], "voice_actor": "Jillian Ashcraft" }
It works, but there are a few things I'd change.
First, the name should be Capitalized, so it returns Monika instead of monika.
The age is alright, they're all 18.
born_date, while personal choice of a name, i would rather change that to birthdate, as that is usually most commonly used to refer to the day someone was born.

However, I noticed you added these for the three other characters, and I believe you've been misled, as none of these characters have actual official dates. So for Yuri, Sayori and Natsuki, these should be removed to not mislead people. Only Monika's is known so far.

Concept height is good, but I'd change from string to integer for easier usability

Hair color and eye color is fine imho, but I would suggest using a hex code, but as they are, is fine.

Voice actor is cool.

I noticed your "no character found" error response, which I believe could be swapped out for simply sending back a 400 HTTP Bad Request code instead.

On poems, they're alright, but I noticed you have a translation variable. No idea if you planned to fix this later, but I'd change how these work if thats the case. Maybe add an alternative request handle if you want a specific translation of a poem in a specific language.

The only thing that sticks out to me is the occasion field. Its a bit clunky, but it works. I'd change from string to integer to indicate which day instead.

A suggestion I propose is a font field, where you can specify the Doki's font, if that is useful to someone.

Have a nice day!