The most straightforward answer as to why there are services listening on IPv6 addresses is that your system has at least one IPv6 address assigned to it, and some services are set to bind to all available IPs rather than specific IP addresses (which is what most services tend to do by default). So in the case of sshd, for example, it binds to TCP port 22 on all your available IPv4 and IPv6 addresses, which is the meaning of the 0.0.0.0 address in the case of IPv4, and of :: in the case of IPv6.
If you do not want services to be reachable on an IPv6 address, then you have a few choices:
Configure the service in question to only bind to the specific IPv4 IP addresses or interfaces you want it to use
Firewall off the IPv6 addresses or ports that you do not want people to be able to connect to
Disable the IPv6 addresses or interfaces on your system that you do not actually want to use
In terms of how you'd kill these connections; your fuser syntax doesn't seem quite right there, no. Normally you wouldn't want to literally "kill" anything anyway, unless you were dealing with a process or service that was not responding to normal controls.
What you will want to do is use the correct command for the service in question to stop it or shut it down (e.g. systemctl stop sshd.service to shut down your SSH service on a systemd-enabled Linux distribution, for example). You could not kill the processes that are listening on the IPv6 addresses specifically, since (if you check your list) you'll see that the PIDs for the listening IPv4 and IPv6 ports are the same, since it's the same process doing the listening in each case.
So, in summary: if you actually don't need or want to use IPv6, the simplest thing is just to disable it for your operating system entirely. If you need it for some things, but not others, then either configure the services you don't want to use IPv6 to only bind to IPv4 addresses, or alternatively firewall off incoming IPv6 connections to those IPs and ports you don't want people to be able to reach.
The classic fuser command works on files. In Unix many things are implemented as devices that are special files and behave like files.
But network is implemented differently; you need other commands.
In Linux a p option lists associated processes
netstat -luntp
ss -luntp
In Unix it might be impossible, or there is an OS-specific way to get the processes.
Maybe you can install lsof that can do more than fuser.
Enabling/disabling IPv6 is OS-specific, too.
If you tell us your OS, then we certainly can tell you more. Try to get the OS from
Besides @drysdalk answer: if you find ports which you don't want to open at all, whether in IPv4 or 6, find the service that listens on it and disable, or even uninstall.
For example: I don't want SSH port open on my home computer, so I just make sure openssh-server is never installed. Or, if I need it, but only sometimes (like rsync'ing files between computers at home), I disable them with systemctl disable sshd.service, then stop them in the current session with systemctl stop sshd.service.
you shouldn't let mysql listen to any (:::)) address, that's a very bad idea. Unless its port 3306 is protected by a packet filter, like e.g. nftables or pf.