You haven't read the documentation properly.
It clearly says that all requests are to be made to the base url
https://hummingbird.me/api/v2
Followed by the method.
That being said,you should make this change to start seeing results
$url = "https://hummingbird.me/api/v2/anime/1";
Edit:
I edited your code after reading httpful docs. That being said, i have no experience with httpful, my knowledge comes from its documentation, so im not exactly sure how to grab the response hence i used var_dump.
I've tried the same request using curl class, and i get a json response.
This should give you a successful request using httpful.
$url = "https://hummingbird.me/api/v2/anime/1";
$response = \Httpful\Request::get($url)
->expectsJson()
->addHeaders(array("X-Client-Id" => "0fd2edceaaf120093b78"));
->send();
var_dump($response);