Raid Boss

Raid Bosses (レイドボス) are powerful Heartless which appear in Kingdom Hearts χ[chi] and Kingdom Hearts Union χ. They attack the hub in Daybreak Town at certain intervals and have to be defeated by the 's and rival teams to defend the town. They are the main source of Lux, making them an essential target for winning the daily Team Battle (チームバトル) and weekly Union Ranking (ユニオンランキング).

Story
While a Raid Boss is attacking Daybreak Town, the sky is covered by clouds of darkness.

Kingdom Hearts χ[chi]
The Raid Boss changes every two or three weeks.

The first attack on a Raid Boss is free, but further attacks require the Player to spend Battle Points (BP). The damage dealt to the Raid Boss is dependent on the BP spent, the Chain Bonus (チェインボーナス) awarded based on how many allied players have already attacked the boss, and the Keyblade Bonus (キーブレードボーナス) awarded based on using the Keyblade that the Raid Boss is weak to. The damage dealt can be multiplied by 10 by triggering the EX Card Bonus (EXカードボーナス).

Each Raid Boss is accompanied by a rarer variant that drops more valuable rewards, usually named Ω (亜種), which has a chance to appear when the initial Raid Boss is defeated quickly enough.

Kingdom Hearts Union χ
The Raid Boss appears depending on the mission in which it's summoned. As of the 1.1.1 update, there are six Raid Bosses, each with an "Omega" counterpart, that spawn during story and daily missions. It appears after a Mission once the player has defeated their 82nd Heartless since their last Raid Boss. A Raid Boss typically costs 10 AP to attack, with the one who caused it to appear getting a free first hit. After they die for the first time, the boss is then available to the rest of their party to attack. There's a time limit of 10 minutes for most bosses, extended to 20 minutes for some Rare event bosses and Omegas. Typically, a raid boss will knock out the player once they're out of free turns, unless it's an extremely low level (1-2) or Second Chance activates. The primary goal is to destroy the target's limbs, gaining free turns, and then to destroy its torso.

Players gain one to three rewards after defeating a Raid Boss, split into three categories: Victory, MVP/Host, and All Points Defeated. The rewards received are randomly chosen from a group of two to four items, which change depending on the Raid Boss's species and level. You can check these items by tapping your raid boss or long-pressing your party's raid boss. Starting around Story Quest 131, a Rare variant of the Raid Boss has a small chance to appear. It's stronger and typically has multiple elements, but also has better rewards. The players in a party will get a notification once one of them has summoned a Rare Raid Boss.