The Calendar is an important aspect in the Persona series.
The calendar is a major component in the Persona series' Daily Life system. Time affects availability of certain activities with the inclusion of permanently unlocking them, as well as dictating important deadlines for the protagonist to follow. Some events may take place during a specific time of day, as well as days of the week.
Initially, a majority of Tartarus is locked from use, with certain roadblocks being automatically cleared off each Full Moon. However, aside from training for the next unskippable boss battle, climbing Tartarus seems to purposefully lack any major significance early on. This is turned on its head during the end of the game, where SEES must reach the very top of Tartarus by the last Full Moon.
In the Persona 3 series only, certain party members might be unavailable during visits on Tartarus on pre-determined days.
Persona 4 introduces the Weather system, which has an effect on the availability of certain activities in the protagonist's daily life, similarly to the time of day or the day of week. However, compared to time, the weather is more flexible and during a normal playthrough, is harder to predict.
In the Persona 4 series only, the weather serves as a deadline for the Investigation Team's rescue missions: during the next foggy day, the respective victim thrown in the Midnight Channel will be killed, with their body found in the real world soon after. However, the nature of the weather makes it difficult to estimate when the upcoming foggy day will arrive--worse, weather forecasts do not report on fog.
- Main article: Calendar (Persona 5)
Unlike previous entries, the deadline system isn't based around natural events. Instead, they're based around the schedule of their targets, where they have to infiltrate their Palace and steal their Treasure before a specific date in order to prevent them from harming the group, and reform them in the process.
The weather system from Persona 4 returns back in Persona 5, but no longer plays a major role in deadlines, only activities and battle criteria. Also, additional information has been added, like "heat wave" or "flu season."