A pact (契約 keiyaku?) is the partnership between two Players during the Game. Neku has 3 possible partners: Shiki, Joshua or Beat (depending on the chapter). Symbolized by the Puck in battles, the pact is not simply an agreement; it is a binding force between two Players, and its benefits are vital to their survival in the Game. These benefits include the ability to activate psychs and the prevention of unwanted battles with Noise (except those set upon them by Reapers and Taboo Noise). A Player whose partner is erased has seven minutes to make a new pact before being erased him or herself. As any nearby Player will probably already have a partner, erasure is almost certain. Pacts can also be formed with certain objects, such as Beat with Rhyme's pin. Harrier Reapers may form a pact with another Harrier, and a Puck will travel between them in battle, but often, they will fight alone, presumably making a "pact" with their own shadow, hence why they are not consumed by regular noise and granting them a shadow doppelganger to help them fight. Additionally, Harrier Reapers may also form pacts with unpartnered Players, as Beat did with Neku. Megumi Kitaniji also hypnotized Shiki into making a pact with him (although this was highly unusual). It's also implied that Beat made a three way pact with Neku and Rhyme's Noise pin as he's shown to still have Rhyme's noise form with him.
It's implied that its also possible to make pacts with Noise. This is shown when Sho Minamimoto appears to be in some kind of pact his Taboo Noise as it appears with him in his boss battle in place of a shadow doppelganger. Later he even merges with his Noise form to gain a huge boost in power. The most notable Noise pact is that of Beat and Rhyme (In her Noise form). They still have the pact from when they were both players. Though Rhyme does not actually appear at any time during the fight she seems to give Beat a huge increase in power. Later they team up with Neku allowing him to use Pin 262.
A pact is required to activate any psych abilities and protect the Players from unwanted Noise. Without a pact, Neku cannot deal any damage and his only option is to escape from battle. The only exception is in the final battle, where Neku fights alone (Though this is arguable since Shiki, Joshua and Beat actually do appear on screen during the fight) . Upon dealing enough damage, the player can 'reform' a pact with a released partner, giving him a light puck. Upon releasing all 3 partners, Neku presumably forms a 4-person (five person if you count Rhyme/Pin 262) pact, allowing him to unleash a powerful attack reminiscent of the Reaper Symbol.
- According to the manga by Shiro Amano, a pact between Players is established by holding hands (as Neku and Shiki did in the first chapter of the manga). However, this is debatable as other kinds of pact (with pins/objects, with own's shadow, etc.) are certainly not viable through holding hands- such as how Beat made a pact with Rhyme's pin (Pin 262). Still, the basic rule to form a pact might be to simply touching each other, regardless of hand or any other part of the pact maker's body.
- No indication is made in-game about the exact requirements for pact formation. However, when Neku formed pacts with Shiki and Beat, both Players explicitly stated that they wished to engage in a pact on Day 1 of their respective games. Neku's pact with Joshua, however, breaks this convention; Neku is surprised by the formation of a pact and offered no consent.