Technically, it's also possible to use non-database tools like zeromq (which are more suited for this purpose since they don't use a persistent storage if your data aren't permanent), or even host the web server from the plugin directly. If you want to share real time data, these would be better options. (But kill counter is persistent data, not real time data, so it doesn't matter here)
Technically you could just make a console application that says, "imagine some players joined your server and you are respected as a server owner and have supreme power..."