Unlocking this character will most likely require several trips through the Gungeon.
Unlock Hint 1: Before anything else, you need to have successfully killed the past of one of the first 4 characters.
Unlock Hint 2: This character will sometimes be encountered in the Gungeon! However, they are found with only 8-25% chance, more likely in the lower floors. Be careful not to mistake them for someone else, say an enemy. You don’t have to talk to them, but you’ll need to find them a few times.
Unlock Hint 3: Have you noticed that on occasion a specific “enemy” appears among the others, but does not attack you at all no matter what? Be sure to return the favor and spare them too. A few times, actually.
Unlock Hint 4: This specific “enemy” wears a red cape and wields a simple gun.
Unlock Solution: The character is a red caped bullet kin that appears alone or in a group. They are found with only 8-25% chance, more likely in the lower floors. They will run around but not attack the gungeoneers. Don’t attack them and wait until they teleport away. You will need to do this 5 times in total before the Bullet shows up in the Breach, “sleeping” at the left of the Pilot