Pins can be carried in their own inventory, which is separate from the Item inventory.
The Pin inventory is divided into two sections: Mastered (which contains mastered pins) and Stockpile (which contains the rest). The Mastered section has one slot for every pin (304 slots total) and multiple copies of a mastered pin are stored in the same slot, up to 99 of one pin.
The Stockpile section can only hold 200 pins at maximum. If at any point you obtain more than 200 pins, the next time you access your pin inventory, you will be unable to leave until you have discarded enough pins. The message you will receive at this point is, "Your stockpile is full! You can only hold 200 pins in your pile. Discard xx more pins from your stockpile folder or your decks."
Pins can also be equipped in one of four decks (in that case, they disappear from inventory). The deck size varies through the game; it starts at 2 and can grow to 6 slots as Neku acquires (S) Extra Slot swags.
Pins cannot be moved to or from the deck during combat (including between reductions of a chain).
Pins are used (only) by Neku to:
Only pins equipped in the deck can be used in combat. Some pins enable Neku to perform a variety of offensive or defensive combat functions; others affect the power of other pins. There are also pins that have no use in combat or have purely detrimental effect; these pins would still be equipped sometimes for purposes of evolution or to meet an objective.
The ability that each pin gives Neku in battle is called a psych. When controlling Neku in battle, the player makes use of various types of stylus actions which range from just touching the pin, to tapping the screen, to drawing circles. Each pin is activated by a specific stylus action.
The order the pins are placed in the deck is important. If there are two pins that can be activated with the same stylus action, the one further to the left in the deck is the one that gets activated. This feature can be affected by the use of subslots, available with (B) Sub-slots.
You can change the way your pins are arranged on the screen during battle. First, pause the game. Then you can drag the pins around with the stylus and place them wherever you want. If you press Select, they go back to their default positions (at the top of the screen, in order of pin slot from left to right).
Payment for quest items is made by simply trading the specified pins to the shop assistant, according to the price shown. However the pin must be fully mastered before you can trade it.
Exchange for yen is done by dragging the pins to the trashcan icon in the pin screen. The amount of yen received equals the value of the pin (shown in the in-game pin description). The pin, of course, completely disappears.
For details, see Tin Pin Slammer.
Neku obtains pins by defeating enemies, by buying them from shops, by receiving them as rewards for various game events (e.g., defeating certain enemies, meeting Reaper Objectives, completing side quests), and by evolving them (see below).
Pins also accumulate PP (Pin Points). When a pin accumulates enough PP, it will level up and increase in power, giving greater effectiveness against enemies in battle.
When a pin reaches a certain level it will either evolve or become mastered. A pin's maximum level is given in its pin description; some pins can evolve before they reach maximum.
If a pin is mastered, its level will be shown as a star, it will move to the Mastered section of the Pin menu, and it will be usable in various game situations that require a mastered pin.
If a pin evolves, it disappears completely (including from the Pin Collection results, if you don't have any more of these pins left). Instead, a new pin appears in your inventory, according to the evolution rules described in the pin list and the evolution chart. The new pin has level 1 and zero PP accumulated.
A pin evolves if, by the time it maxes out the PP, the correct PP type is dominant, so remember: once mastered with another PP, it can not evolve anymore. Which PP type is correct for each evolution is shown in the Pin List. Some pins can evolve into different pins, depending on which PP is dominant. Some pins cannot evolve at all; they will become mastered when the PP reaches the required level.
Each pin has an identification number, which ranges from 1 to 304.
For details, see Class.
Any pins of the top 3 most popular brands in the current District will get attack bonus, as specified in the fashion chart. Any pin of the least popular brand will suffer a penalty to attack.
Any pin whose attack is affected will be marked by arrows in the screen during combat. The attack bonus is applied according to the formula given in Damage.
The number of levels the pin has; when the highest level is reached, the pin becomes mastered, or may evolve with the correct type of PP. Many pins, with the correct type of PP, evolve before reaching the maximum level.
The pin can only be used for a certain time or number of uses until it needs to recharge. Not all pins recharge, some are for a one time use only.
The amount of time the pin takes after the start of a battle (or the first reduction in a chain) before it is ready for use.
The amount of time the pin takes after being used up completely, before it is again ready for use.
The amount of yen obtained from exchanging this pin for cash.
See Growth Speed
See Growth Bonus