Lockdown (独房送り, Dokubou okuri)? is a mechanic in Persona 5.
Lockdown is unlocked when the Strength Confidant reaches rank 3. It allows a Persona to stay in the Velvet Room for training, gaining new passive skills. The time for training completion depends on the Confidant rank of the Persona's corresponding Arcana, shortening with increased rank; when uninitiated it takes five in-game days, while at max rank it only takes two days. Any days where major plot events occur do not count towards the Lockdown timer.
While a Persona is in Lockdown, it cannot be used in battle, gain experience, or be used for fusion until the protagonist retrieves it. If it remains in Lockdown for more than 10 in-game days, the Persona is lost. However, Caroline and Justine will inform the protagonist via his phone once he's reached the deadline for releasing a Persona. Accessing the Velvet Room doesn't consume a time slot, so there is nothing to be lost in collecting his Persona.
The skill learned from Lockdown will, most of the time, be specified to cover an elemental weakness. For instance, a Decarabia is more likely to learn Dodge Phys or Resist Phys than other resistance passives. If a Persona has multiple weaknesses, the skill it learns will select a random weakness to cover. Rarely, Dodge/Resist passives of elements that are not the Persona's weakness, or even passives that resist ailments; raising the rank of the corresponding Confidant will reduce the chance of this happening. There are no passive skills that can cover Gun weaknesses.
If a Persona already has a resistance/evasion passive, even if said skill isn't covering its weakness, the passive it gains from Lockdown will be randomly determined, up to and including ailment resistance passives. This also applies if Lockdown is used on Personas without any innate weakness. The type of skill to be gained is decided once the Persona commences its detention; if the Persona picks up the wrong skill, reloading to just before its release will not change it.
At Strength Confidant rank 8, Personas left in Lockdown will begin to learn Null and Evade passives.
Persona 5 Royal
In Royal, the weakness-covering skill that the Persona can learn depends on its Level.
Additionally, it is now possible to light incense while a Persona is in Lockdown, granting points towards a specific stat. For example, using a Nirvana EN incense will increase the Persona's endurance by three. There are also types of incense that increase two stats at once. Incense can be bought from the Home Shopping Program, Jose's Shop and the Mantra Ganda Incense Shop in Kichijoji. The time taken for the incense to take effect is 2 days.
The effect of incense is doubled during a fusion alarm.