Hi,
In cases like you, unfortunately the nature of wp’s url, you gonna have to add the rewrite rule yourself.
You can have a look at add_rewrite_rule.
https://codex.wordpress.org/Rewrite_API/add_rewrite_rule
So, your code will look something like:
function custom_rewrite_basic() {
add_rewrite_rule('^mangas/([^/]*)/([^/]*)/?', 'index.php?chapters=$matches[2]', 'top');
}
add_action('init', 'custom_rewrite_basic');
Cheers
