Events are a period of time where a special dungeon is available that allows you to earn unique currency.
Each event has a 5 star flower knight that can be earned and fully upgraded without spending any real money. This girl is referred to as the event 5 star girl/flower knight. Events tend to host the appearance of one new 6 star flower knight and three new 5 star flower knights. A Premium Gacha becomes available which increases the rate of the new flower knights appearing if you choose to roll it. The event 5 star does not get featured in this gacha because event 5 star flower knights are not earnable from gacha. 4 star girls released during the event are also not featured in the Selection Gacha.
The usual format that events go through is as follows. Events last for two weeks. During the first week, only the first half of the stages and event prizes are available. During the second week, the second half of the event contents become available. Event currency is earned more efficiently in the newly released content, but the cost of the prizes available for the newly released content is also higher.
Event stages are divided into four difficulties: elementary level (初級), intermediate level (中級), high level (上級), and top level (最上級). There are eight stages total between the first and second halves of the events combined. These stages are referred to as E1 through E8 as shorthand. All event stages can generate Raid Bosses or Secret Gardens, but some event stages have unique Secret Gardens that produce a large amount event currency. A Secret Garden may be referred to as BS as a shorthand for Bonus Stage.
Each event has its own unique type of currency that can not be used for other events. The currency is earned by crossing over map panels with that currency in event dungeons. How the currency is used depends on the event.
Although events only last for a certain amount of time, those events will eventually return as a republished event (復刻イベント) for a limited time. A republished event lets you replay the event stages. The chests in those stages only drop sealing stones which allow you to earn and fully power up the flower knight that was featured during that event. Other features of the event such as unique raid bosses and gachas will not be available.
Past republished events will eventually return again as a re-republished event (再復刻イベント). A re-republished event is available indefinitely, but the efficiency of earned seal stones is reduced. Seal stones earned from the republished events won't be carried over to the re-republished event.
All events have currency which you can earn from panels in the event stages.
Card Flip events use panel currency to flip cards hiding items.
Gacha events use panel currency to roll an event gacha with a set number of rewards.
Level Up Boss events use panel currency to let you fight turn-limited RBs.
Raid Boss events use panel currency to summon RBs. Fighting and defeating them earns you a different type of currency which can be used to buy things from the Wares.
Swanboat Race events use panel currency to bet on daily races. Winning bets earns you a different currency for buying Wares.
Treasure Rally events use panel currency to move along linear boards full of items.