[allhailhata]

"International anime fair"
Just go to Lawson after arrival.Maybe no fear of sold out.

"a concert at the Zepp Tokyo"
Did you check the right side of the page? "Eventer info"
There are links.Check the page.They tell you how to purchase and reserve
tickets in JAPANESE.

Usually,You can buy concert tickets at convenience stores.
Of course ,there is a fear of "sold out".How to reserve? You must registar with Ticket websites.Unfortunately they are in japanese like Lawson ticket.
If you can reserve,you can usually receive ticket at convenience stores.
Asking your friend who can understand Japanese to reserve is a reliable means.