For your information.
About JAL's complicated lounge access
See
http://www.jal.co.jp/en/inter/lounge/japan/nrt/
Bottom of this page shows lounge scheme of JAL.
JAL has paid membership service known as JGC(JAL Global Club).
JGC has separate lounges.
Even if you are top tier JMB Diamond member (100,000 miles+),
You can not access JGC lounges.
Sakura Lounges are Business class lounge equivalent.