You have a good memory. According to my file, Itachi Susano'o has only been available through one coupon event in the last 3 years, during the week of Dec 19, 2019. He cost 108 stars, which came out to ~800 coupons for each frag at the time.

FYI, He is the second most expensive coupon ninja I have in my data. With Madara Founder being the most expensive coupon ninja ever @1847 coupons per frag the one time you could redeem him in an event.