After being unable to for so long, Naofumi finally gets to upgrade his party's classes. He then takes part in a meeting of the Four Cardinal Heroes, held under the guise of a celebratory banquet. There, he learns of the existence of a bonus stage, with increased XP earnings. Meanwhile, Raphtalia gets into a fight at the party.
we mean the once-in-a-decade event where
نقصد الحدَث الذي يُقام مرّة في كُل عشر سنوات
qui se produit une fois tous les dix ans
et où il est possible de gagner
è un evento che avviene ogni 10 anni
é um evento que acontece
uma vez a cada dez anos
Раз в десять лет… 
опыт, который можно там заработать,