There is an annual big music event by Avex Trax. This music event is called "a-nation."
This year's a-nation concerts are scheduled to be held at Ajinotomo Stadium of Tokyo on August 25 and 26, and at Nagai Stadium of Osaka on August 18 and 19.
Music artists currently expected to be invited to 2012's a-nation concerts:
AAA (Triple A)
Sandaime J Soul Brothers
Acid Black Berry
Do As Infinity
Shonan no Kaze
Ayumi Hamasaki: she will appear only on August 26 (the final day)
ELT (Every Little Thing): ELT will appear on August 18 and 26.
Big Bang (South Korean band)
Toho Shinki (South Korean band)
Note that all of these artists will appear only on a specific date. There is no artists who will appear on all days.
All a-nation concerts (those on August 18, 19, 25 and 26) will start at 15:30 and continue until night. You can enter the a-nation concert even 2 hours earlier than the start time.
Admission fee: 9,800 yen (expensive!) This is an advance ticket fee. Day ticket fee might be different. If you buy a day ticket from a scalper there, you will pay more.
Unfortunately, advance tickets for almost all a-nation concerts are going to become not available today's midnight or tomorrow's midnight. Here is its official announcement (written in Japanese):http://a-nation.net/ticket_sf.html
If you definitely want to see Ayu and ELT, get a day ticket in front of the Ajinomoto stadium in the early morning of August 26. You will see then so many people are standing in line to get a day ticket. Staying in front of the stadium overnight might be needed to get a day ticket.
Here are several YouTube videos showing previous a-nation concerts:
AAA (2009's a-nation concert)http://www.youtube.com/watch?v=eph5twTLsyY
Girl Next Door (2010's a-nation concert)http://www.youtube.com/watch?v=osjdARwMjx8
As you may know, Girl Next Door is a popular Avex Trax band of one girl-vocalist and two male musicians. This band's most popular songs are Infinity and Dadapara (my recommended songs):http://www.youtube.com/watch?v=he2G8FbqGtchttp://www.youtube.com/watch?v=-f0AYlFvW6E
Ayu (2010's a-nation concert)http://www.youtube.com/watch?v=GR1Y8-eIa9c
Do you know how to access to the Ajinotomo stadium? Do you plan to stay in Tokyo on August 26 or in Osaka on August 19?