Martinist King is a browser extension designed to cater to fans of Mateni, a bald, single real estate professional in his 40s from Chiba Prefecture. The extension aims to determine the king among Mateni fans by promptly notifying users of his streaming status.

During the time frame of 8:00 PM to 1:00 AM daily, the extension checks Mateni's streaming status every 10 minutes. If a new stream starts, it sends notifications and automatically opens the broadcast page in a new tab. As of version 1.0, the extension supports notifications for [YouTube, Nico Nico Live], although currently, only Nico Nico Live notifications are functional due to the absence of Mateni's YouTube channel.

The latest update (ver0includes changing the link destination for the privacy policy to GitHub Pages. Previous updates introduced features like a test button for the notification function and voice acquisition for rare broadcasts by Mateni, along with bug fixes for behavior when a broadcast page is already open and issues with saving settings when pressing switches directly on the options page.