Hi! Thank you for giving us your feedback in regards to One-Ingot Sales. I will let the team know in regards to the 500 coupons being made only available to the those who participate early as it is limited to 30 phases, making it rarely available to anyone who participates later.

In regards to One-Ingot Sales with the coupons as an option and synergized with Fukurokumaru's Deal. This has been done before. One of the very first time it was done was on November 8th, 2018. One-Ingot Sales is designed to primarily give players the ability to invest into the event with the chance to obtain a reward at sometimes potentially a fraction of the cost. With the chance increasing based on the amount of participation from each individual player for a specific item (during a specific phase). Due to the nature of one of the options in One-Ingot Sales being coupons, players definitely can invest into One-Ingot Sales in order to use the coupons to invest into Fukurokumaru's Deal.