Item Trading Side Quest - Dark Cloud
There is only a single unnamed Side Quest in all of Dark Cloud and it involves trading various items to different NPCs in each of the towns you visit throughout the game. I call this quest the Item Trading Side Quest considering the main objective of this quest is to trade various items to different people.
You can start this quest in either Norune Village or Matataki Village, depending on your choices. In Norune Village you may receive a piece of Candy from Claude by 100% completing his house and watching the Event that takes place here. Alternatively, you may be given Candy by Couscous instead who is in Matataki Village by 100% completing his house and watching the Event here.
Essentially whomevers house you 100% first and watch the event at is who you'll get the Candy from. Once you have the Candy you'll have to trade it for the Ointment Leaf which you'll then trade for Foundation and so on and so forth. Below are all 5 steps of this quest and who you have to trade each of the items to.
Candy: Candy is given to you by either Claude in Norune Village or by Couscous in Matataki Village as a reward for 100% completing their house. Both of these NPCs can give you Candy, it doesn't matter which you get it from.
Ointment Leaf: Bunbuku in Matataki Village gives you this item as thanks when you give him the Candy. You have to 100% complete Bunbuku's House before you're given the option of trading the Candy to him. The event that happens when you complete his house is when you'll be giving him the Candy. Kululu, the person who lives with him, will be up on the rafters in the house and will only come down when Toan offers up the Candy.
Foundation: Give the Ointment Leaf to Basker in Queens and he'll give you the Foundation in return. Much like with the previous items you need to 100% complete his house before he'll give you this item.
Clay Doll: Trade the Foundation to Jibubu in Muska Lacka for the Clay Doll. You will need to 100% complete Jibubu's House, watch the Event then come back later before he'll trade you anything.
Once you have the Clay Doll item all that's left is to take it to the Yellow Drops town which is on the moon and trade it to one of the Moon People standing under an arch (pictured below). He asks you for an artifact of the moon people and surprisingly enough this is one of them. Your reward for the Clay Doll is the very rare Sun Attachment which gives you +10 Attack, +10 to all Elements and +3 to all Anti-Monster Attributes.
The Sun Attachment works exactly like any Gem or regular Attachment does and it's up to you if you'd like to fuse it into a weapon or hang onto it and trade it between weapons for the bonus it gives. It's only marginally better than most of the Gems that you can get for a weapon, in my opinion.