Introduction
This is just a quick step-by-step walkthrough of everything needed to see the ending of this game.

Walkthrough

-When you spawn into Lyria, go to the tea shop (the shop on the right) and buy some Chamomile Tea. Bring it to the old man behind the desk in the library of Lyria. He should say something thanking you for bringing him the tea.

-Pick up the Shard of moonlight 4 from the altar up some stairs in Lyria.

-Use the left crystal in the teleport room to go to the mines. Go through the mines until you find a room with a ring that will give you the Fire Wave spell when you interact with it. In this room, you can also find a corpse with a key on it that will allow you to open the iron gates in the area.

-Open the iron gate in the area with mushroom enemies and it will lead you to an area of the map with zombies running around. Go through this area until you find an NPC that will initiate dialog when you get too close to it. In this room you can find a crystal shard on a corpse that will allow you to warp back to Lyria, which you should do.

-Use the middle crystal in the teleport room to go to Laetus Keep. Go through the area until you find an old man sitting on a box by a house. Either kill this old man or exhaust his dialog until he asks you to do a quest for him and do the quest. Either way, you should get a mark of royalty from him afterward which allows you to open the green magic doors in the area by pressing the interact key in front of them. It's also an accessory that you can optionally equip for minor HP regen, but you don't need to equip it to open the magic doors.

-Open the green magic door which leads to the actual Keep area. Go through the keep until you find a cutscene about a fog beast. Once the cutscene is over, enter the entryway behind you then open the chest at the end of the hallway for the Water Crystal. Go back to Lyria.

-Go back to where you gave the tea to the old man in the library. He should be asleep and you can take the Aquarius Key from his sleep-corpse. Use this key to open the iron gate in the library and enter the Aqueducts.

-Go through the aqueducts until you find the watersmith's key. You can use the key to open the doors with keyholes here. Progress until you find the Harp of Harmony. After you find the Harp of Harmony, use it from your inventory and magical floors will appear over various pits in the area, which you can use to go further into the dungeon and find the Ring of Fog. Go back to Lyria after finding the Ring of Fog.

-Use the right crystal in the teleport room to go to the Road of Ruin. On the pedestal in this area, use the Water Crystal to open the door.

-Progress through this area until you find a lever. Pull the lever to open a sealed gate into the castle, where you must kill a griffin to unseal some doors. Afterward, progress through the doors into the castle proper (which changes maps).

-Do the dungeon, finding 4 shards of the moonlight sword along the way. One is in an ornate chest, one drops from an enemy called an Ankou, which is a headless skeleton with a scythe (so kill every one of those you see). One drops from the dungeon's boss, which will spawn upon opening an empty stone chest in the prison area and then heading towards the exit. The remaining shard is given to you by an NPC in the prison once you open his cell. Go back to Lyria.

-Speak to the NPC standing in the garden area right across from the shops until she forges the Moonlight Sword for you. Then, take the Moonlight Sword and the Ring of Fog to the altar where you picked up Shard of moonlight 4. Interact with the altar.

-Talk with the NPCs while walking in a straight line if you wish, then stand in front of the obelisk to go to the ending sequence.

-Interact with the coffin in front of you and go to sleep, and you will have reached the ending of the game.

Thanks
Thanks to Kira for making a very interesting game.
Thanks to you for reading this guide.
Thanks to my cat for existing.