In okinawa,folks get together in front of the family graves once a year on april or may. This is one of the okinawan traditional celemony named"si-mi(seimei-sai)". Regendaly,the purpose of this is to pray for the ancestors and celebrate families prosperity. Nowadays, the reason why we get together seems  rather for our leasure.Chatting,eating and drinking with our ancestors.It's just like picnic. It is not easy for us to take time and prepare many things (make and gring  plenty of fiest,etc),neverthless, it is the enjoyable time of the year.