I'm curious as to why we are able to purchase and use onigiri coins in client, during a phase where our progress will be wiped? Is there going to be an equipment wipe exclusively? Is this an intended feature? I'm not understanding entirely - It seems to me like essentially wasting a players time/money.

This is a pre-purchase campaign.

Coins will be given to you once the official service starts, along with bonuses for early purchase.