That is for ping. ICMP v6 REQ: REQ means request and is a NAT type of terminology. A firewall rule allows some form of inbound traffic - here ICMP ping inbound (REQ), and then creates a state entry which allows the corresponding return traffic (RESP or response) - pong!
ping can be useful to determine connectivity and that rule will not open you up to anything nasty.
Your router seems to have been designed by someone who gives a shit about security, which is a good sign.