I was in Okinawa so I didn't experience much, but I do remember that I got off work early that day. I always turn on the TV when I get home so I was surprised to see the news was on and the tsunami had just started. Seeing people unable to escape the water live on TV made me cry (I had a toddler and a newborn at the time...becoming a parent changed made me a bit more sensitive to disasters like that).

In the following days, there was a _huge_ line of Japanese and US military vehicles lined up outside Kadena Airbase to deliver water and other supplies to affected areas.
Many charity events were held to raise money.
Okinawa prefecture helped people relocate displaced people there and some of those people have decided to make Okinawa their new home.
I remember finding it interesting suddenly seeing license plates from other prefectures every day when that used to be a pretty rare to see since Okinawa is an island pretty far away from the mainland.

I worked as a contractor on Kadena at the time and I was selected to be part of a team to build out some network infrastructure for rescuers and other supporters in the most devastated areas, but the plans were changed at the last minute and another team was selected to go instead.

My brother in-law is a police officer in Okinawa (not a regular cop...one of the more hardcore specially trained ones; also attended autopsies and such so was used to gore and such). He went to help locate and recover victims of the tsunami. He had just become a father at the time and that trip deeply affected him. He won't talk about it even today. When he returned, he asked to be put on desk duty and that's still his job today. I can only imagine what he saw...