well,,,, an exact date isn't disclosed since I have terrible memory, but I first opened the game during farewell my mask period; I think the time I actually started maining sekai was during hello to a new day though (<- i lost that en account).

my jp account was pre-ena5 (so around tpor period); though I started mainly playing during ena5 to get mzen cards. I was a niigo fan before and I got both in singles

my new ensekai account started during anni4 (dreamstage)