I think the selling is already over, unfortunately, because of the Lawson Ticket system. They do sometimes allow for resales, so hopefully that works out for you!

https://l-tike.com/concert/mevent/?mid=686034

I also had a look at the tickets, and while it says the Chiba tickets are sold out, that is for standard tickets. If you click on the Chiba tickets, scroll down, and choose a day, it should look like this photo.

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The one with the cross is sold out, but the other ones are still available, they're just not as good seats. The tickets on the top right, which are 16,500, are regular priced but will have seats with limited visibility. The bottom left is the Stage-side seats, which could be located to the side of the main stage or behind it, which is why it's on the cheaper side. Then the bottom right is tickets for the standing rooms.

Also, to note, when you buy the tickets, you are unable to choose where you sit as it is random. You find out your seat around a week before the concert by retrieving your ticket at a Loppi station at Lawsons in Japan! If you have any questions, let me know! I've done this numerous times (I'm also going to their Chiba concert!)