proxy_cache_path /path/to/cache levels=1:2 keys_zone=pximg:10m max_size=10g inactive=7d use_temp_path=off;

server {
    listen 443 ssl http2;

    ssl_certificate /path/to/ssl_certificate.crt;
    ssl_certificate_key /path/to/ssl_certificate.key;

    server_name i.pixiv.cat;
    access_log off;

    location / {
    proxy_cache pximg;
    proxy_pass https://i.pximg.net;
    proxy_cache_revalidate on;
    proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504;
    proxy_cache_lock on;
    add_header X-Cache-Status $upstream_cache_status;
    proxy_set_header Host i.pximg.net;
    proxy_set_header Referer "https://www.pixiv.net/";

    proxy_cache_valid 200 7d;
    proxy_cache_valid 404 5m;
 }
}

addEventListener("fetch", event => {
  let url = new URL(event.request.url);
  url.hostname = "i.pximg.net";

  let request = new Request(url, event.request);
  event.respondWith(
    fetch(request, {
      headers: {
        'Referer': 'https://www.pixiv.net/',
        'User-Agent': 'Cloudflare Workers'
      }
    })
  );
});