OK.... So I can assign any v6 in my block to a computer.
So I did that, and when I went to whatismyipv6.com it gave me the address of the tunnel. I assumed this is how it would work, but someone who is using tunnelbroker was able to connect to IRC and the /whois came back with his custom IP... So how does this all work?
Thanks for helping me understand btw.
This is due to the way your computer chooses which IP to use as the source IP when it sends out IP packets.
What the other person is likely doing is terminating his tunnel on a router. Then his router hands out IPs in his /64 (or the computers behind the router use SLAAC, either way). As long as the router will correctly route the IPv6 packets through the tunnel, then his computer will choose his custom IP as the source IP because it is not directly attached to the tunnel.