DamonW suggested cutting down the number of globals used throughout Hotaru. Most of these are global objects such as $db, $post, $current_user and $cage. Apparently using so many globals can be a security issue and is bad practice in object-oriented programming because it makes it difficult for other applications to use classes dependent on globals.
So perhaps this should be a priority for future revisions. The question is, what's the best way to go about it?