To access the Abyss in Hollow Knight, you must first defeat Hornet for the second time in Kingdom’s Edge to obtain the King’s Brand. Here’s a step-by-step guide to help you through the process:

1. Defeat Hornet: Head to Kingdom’s Edge and locate Hornet. Prepare for the battle, as defeating her will reward you with the King’s Brand.

2. Travel to the Ancient Basin: After acquiring the King’s Brand, make your way to the Ancient Basin area. Utilize the Stag Station to reach the Hidden Station within the Ancient Basin for quicker travel.

3. Open the Abyss Gate: Once in the Ancient Basin, go left and drop down through the passageway. You will encounter a large gate adorned with the King’s Brand symbol. Ensure that the King’s Brand is equipped, then approach the gate to have it open, granting you access to the Abyss.

4. Exploring the Abyss: Upon entering the Abyss, continue to explore the area. You will find a locked blue door located halfway down, covered in blue vines. To unlock this door, you must possess a total of 15 Lifeblood Masks.

5. Equip Necessary Charms: To achieve the required 15 Lifeblood Masks, equip the Lifeblood Heart and Joni’s Blessing charms. These charms will provide enough Lifeblood Masks to meet the requirement for unlocking the door.

6. Unlock the Blue Door: With the Lifeblood Masks equipped and available, you can now approach the blue door and open it. Doing so will grant you access to the Lifeblood Core charm, which is significant for gameplay in this area.

Summary of Steps:
– Defeat Hornet for King’s Brand.
– Use the Stag Station to reach Ancient Basin.
– Open the Abyss gate using the King’s Brand.
– Equip Lifeblood Heart and Joni’s Blessing to gather 15 Lifeblood Masks.
– Unlock the blue door to obtain the Lifeblood Core charm.

By following these steps, you will successfully navigate through the process to access the Abyss, an essential area for late-game progression in Hollow Knight, where you can find powerful charms.