"Relocated to the other guild" route:
Mission 1 (Any costume): Revisit the village in the southwest (the one with sick people). Talk to the mayor and then go into the mines to rescue the girl.
Mission 2 (Any costume): Head to the mountain and investigate the crack at the end.
Mission 3 (Guild costume): Head to the pyramid, go along the right side of the screen until you see the stairs going down. Follow the path until you see a man on the floor.
Mission 4 (Paladin costume): Go to the temple, talk to the man at the table, go through the door to the northwest portal, follow the path.
Mission 5 (Kunoichi costume): Investigate the cave south of the city. Follow the path to the end as usual.
Mission 6 (Any costume): Return to the temple, talk to the man again, and go to the portal in the northeast. Business as usual.
Mission 7 (Maid costume): For this mission to trigger, you must have the maid costume produced already. Your sister back in the other town makes it. Once you have the costume, go back to the guild building and there will be a girl with a "!" on her head just left of the quest counter. Talk to her, get the quest from the counter, go back to the first town and talk to the weapon dealer for the item.
Mission 8 (Kunoichi costume): Once you pick up the mission, go to the building to the left of the guild building. Once you enter, head right and you'll find the orange hair guild member that you need to speak with to leave for the mission. Once you get to the cave, business as usual.
Mission 9 (Bunny costume): Temple again, but head to the bottom right portal. Explore the castle to the end.
Mission 10 (Any costume): Go back to that very first tower you explored. Head to the portal where you picked up the stone from and it should port you to the fancy castle. Go inside, bottom right portal. Defeat boss, then report.
Mission 11 (Any costume): Make your way to the forest southeast of the village that had sick/kidnapped people. Follow path north and west and loop south to get a pickaxe in the chest. Then return to the entrance of the forest and head to the map directly east of the entrance. Pickaxe on rock, then talk to NPC inside for item.
Mission 12 - FINAL MISSION (Any costume): Talk to the quest lady and she'll ask you if you're ready to leave. Assault the fortress. END
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Accessing the "erotic missions" (can only be accessed if you're currently on the route detailed above):
Basically, you just want to have a decent amount of madness (50+?) and a good amount of lust (which should already be pretty high up considering the madness value). Proceed to fail every single mission whenever you can (some cannot be failed).
Mission 1: Lose to the kidnappers.
Mission 2: Complete the mission as usual.
Mission 3: Lose to the slime. (My game actually bugged here and wouldn't trigger the slime rape after I commit suicide, so I was forced to save the guy. This shouldn't be an issue if it happens to you)
Mission 4: Get assaulted by the tentacles in the wall towards the end.
Mission 5: Lose to the boss at the end.
Mission 6: Complete the mission.
Mission 7: Pay with your body.
Mission 8: Lose to the boss.
**At this point, assuming that I haven't forgotten anything and you fulfill the prerequisites, your character will start saying a few lines back at the guild building and then refuse to take missions from the quest lady. That's your cue to take missions from the man on the 2nd floor for the rest of the route.
All the erotic missions are pretty straight forward and don't really require a guide. You will only ever receive missions for 3 locations - the rich man's mansion in the southwest corner of the city, a bar that you automatically get teleported to, and the brothel just south and west of the guild building on the same map.
These missions require a combination of the maid outfit, the dancer outfit, the gym uniform outfit, the school swimsuit outfit, etc. Make sure to check in with the woman on the 2nd floor to see if you can make any more costumes. Aside from that, it's all relatively self-explanatory until the ending. Have fun!
Side note: Many of these erotic outfits have heart skills to unlock on them! Use temptation on human enemies and then try using the heart skills after you have 250 lust and 225(?) madness. You perform erotic moves on the enemies which add to your list of h-scenes. I think there are 6-7 erotic moves to learn in total.
Side note 2: Some steps may be unnecessary, some steps may be incomplete. These are the exact steps I took to trigger the erotic missions, so if it's not working for any of you, I might have forgotten about something or you don't fulfill the prerequisites.