Seedy CD Optional Dungeon - Persona 2: Eternal Punishment

The Seedy CD starts out as a shop but right after beating Smile Mall during the story you'll be able to unlock the 2F of this place which is a dungeon. It's recommended that you wait until after beating Aoba Park to do this dungeon because when it first unlocks Katsuya won't be a part of your party. Baofu is removed from your party for the next dungeon too.

In order to open up the 2F you'll need to speak with Ixquic at the entrance of the Seedy CD (pictured below). She'll give you a rumor to spread about a 100km/h Hag at The Seedy CD. Once you spread this at the Kuzunoha Detective Agency in Aoba you'll be able to access to the 2F and the 3F.

Your first time here you may notice that there are stairs that go up on the 3F but you can't access them yet... This is because you'll be coming back to this place after finishing the Undersea Ruins. You'll have another rumor from Ixquic at that time and two more floors.

Seedy CD Demon Dialogue Choices

While you're inside of the Seedy CD you won't be able to use your Personas... That means you'll have to rely on Contact, Estoma and your regular weapons. Faust (Level 22) is the highest level demon so you won't have any issue beating everything with your regular attacks.

Our goal the first time we're here is to eliminate the 100km/h Hag who is found on the 3F. You'll want to defeat her as quickly as possible because she will run from battle if you take too long. Once defeated you need to return to Ixquic at the entrance and turn in the quest. You'll be rewarded with an Incense Set, it gives you one of every Incense (items that permanently increase your stats).

Seedy CD 4F - 5F

Seedy CD Demon Dialogue Choices

The 4F and 5F become available after you complete the Undersea Ruins dungeon. Just like before you'll need to speak with Ixquic to get the rumor then spread it before you can get access to the final two floors. We're looking for the 200km/h Fogey, he's a random encounter on the 5F.

In the southern portion of the 4F you'll find an elevator that takes you to a hidden area on basically every floor of this dungeon. Make sure you collect all the treasures you can via this elevator; most of the floors will have something. Once you're done with the bonus treasures and the Fogey head back to Ixquic and turn in the quest for a Legenbright item.

You can use the Legenbright to craft Legendary Weapons. I strongly recommend you use the Item Breeder item to duplicate this before consuming it. If you're on Nate's route you should have two of them by now and Elly's route will have one... Assuming that you did this side quest right when it became available.