First a piece of advice. If you're going for the Bromide or CD achievement, wait until NG+. You need to have them all in your inventory and they don't carry over. Just getting the last one on NG+ will not unlock the achievement (don't make my mistake).

Let's start with the big one. For this achievement you need 40 Gold Medals. At the end of each dungeon you get either a bronze, silver, gold or platinum medal; depending on your performance in the dungeon.

The requirements for gold are:

• 1- Break all breakables in the dungeon (pots, ballons, rocks).
  
• 2- Kill all monsters.
  
• 3- Receive less than 5 damage.

There is a time component, but that counts only towards the platinum medal. You only need gold for this achievement.

Every few medals, the fairy of the spring will give you an item as a punishment (reward). Once you hit 40 gold medals, she will have no more to give and the achievement unlocks!

Only unlockable on NG+ since the last CD only appears then.

All but one of the CDs require you to have 10 of the highest level food and present it to Chai in the inn.

• 10 Yakimochi--> Rich Melodies CD
  
• 10 Ice Creams--> Labyrhythms CD
  
• 10 Spiny Lobster--> Night Music CD
  
• 10 Durians--> Breezy Listens CD
  
• 10 Parfaits--> Earthy Tunes CDs
  
• 10 Eastern Noodles-->Fantasy Frets CD
  
• 10 Castellas--> Chart Burners CD
  
• 10 Tempura Bowls--> Light Ambience CD
  
• 10 Yakisobas--> New & Old Wave CD

The final CD (Best of the Rest) appears in Puck Village in NG+ in the place where you find the vinyl boots on your first playthrough.

This one should also be attempted on NG+

• Bromide 01--> Defeat Koboltan-X in the level 00 door in Caiaphas Forest (NG+ only).
  
• Bromide 02--> Dropped by the Hunter enemy in Superi R. Labyrinth (Easy Course).
  
• Bromide 03--> Salamander’s Den, You need to line the character on the photo cut out until a notification rings.
  
• Bromide 04--> Gnome Protectorate, You need to line the character on the photo cut out until a notification rings.
  
• Bromide 05--> Dropped by the Tea Maid enemies in the last floor of Pneuma's Dungeon.
  
• Bromide 06--> Trade all the armor sets you get from the Fairy of the Spring (need 40 Gold Medals) to Reginev in the Dapne Desert.
  
• Bromide 07--> Undine Land, You need to line the character on the photo cut out until a notification rings.
  
• Bromide 08--> Sylphan Woods, You need to line the character on the photo cut out until a notification rings.
  
• Bromide 09--> Defeat Titan behind the tree where you fight the Demon Lord (NG+ only)
  
• Bromide 10--> Dropped by the Guard enemy in Superi R. Labyrinth (Hard Course).
  
• Bromide 11--> Beat the Zwei Shooting minigame on Hard (NG+ only).
  
• Bromide 12--> Present 10 Ramen to Chai in the inn.
  
• Bromide 13--> Present 10 Turkeys to Chai in the inn.
  
• Bromide 14--> Present 10 Slowboiled Eggs to Chai in the inn.
  
• Bromide 15--> Present 10 Pizzas to Chai in the inn.
  
• Bromide 16--> Present 10 Hard Candies to Chai in the inn.

To get this achievement, you need to hand Makarl 50 Pull Tops and 10 Cans once he's in the Gnome Protectorate. You will then receive the full set of Aluminum armor. Equip it to unlock the achievement.

Here's the general location of all Pull Tops and Cans:

Pavel Gardens

• Central Waterway> 1 Pull Top
  
• Treasure Road> 2 Pull Tops
  
• Fairy Passage> 2 Pull Tops and 1 Can

Caiaphas Woods

• Fairy Passage> 2 Pull Tops
  
• Path to Altar> 2 Pull Tops
  
• Treasure Road> 4 Pull Tops and 1 Can

Klopp Caverns

• Cave Tunnel> 1 Pull Top
  
• Fairy Passage> 2 Pull Tops
  
• Treasure Road> 4 Pull Tops and 1 Can
  
• Path to Altar> 2 Pull Tops

Mt. St. Kenopi

• Lava Conduit> 1 Pull Top
  
• Fairy Passage> 3 Pull Tops and 1 Can
  
• Path to Altar> 3 Pull Tops
  
• Treasure Road> 3 Pull Tops

Aplieste Shrine

• Golden Concourse> 2 Pull Tops and 1 Can
  
• Treasure Road> 2 Pull Tops
  
• Path to Altar> 2 Pull Tops

Temple of Espina

• Hell’s Halls> 3 Pull Tops
  
• Path to Altar> 2 Pull Tops and 1 Can

Serpentina

• Royal Passage> 3 Pull Tops
  
• Relay Point> 1 Can
  
• Path to Lair> 4 Pull Tops

The last 3 cans are obtained through the pet companion widget, you need to be at least level 18 and have completed the Aplieste Shrine before you can obtain the last can.

• 1st can: Left-Left-Right-Left-Beg---Back Home--- Right-Left-Left-Left- Go On-Left-Right-Fight
  
• 2nd can: Left-Left-Left-Talk---Back Home--- Right-Right-Right-Left- Go On-Right-Left-Fight
  
• 3rd can: Left-Right-Left-Left-Left-Talk---Back Home--- Right-Left-Left-Right-Left- Go on-Left-Left-Fight

Just FYI, the achievement is bugged and doesn't unlock. Remember to report it on the bug thread, or it might never get fixed.