Little Witch Nobeta

These 4 are collectibles and the others are hidden that rewards you with consumables and upgrades but you can find them easily assuming you search every nook and cranny parts of any places especially breaking stuffs (I only had 96 items on my first attempt of doing the item achievement). Refer to my guide if you want to double check everything.

Little Witch Nobeta - 100% Achievement Guide

Refer to the Treasure achievements.

Treasure Hunter

Elemental:
2x Counter Magic - 1 > 2 > 3
3x Wind - 0 > 1 > 2 > 3
2x Arcane - 1 > 2 > 3
3x Ice - 0 > 1 > 2 > 3
2x Fire - 0 > 1 > 2
1x Lightning - 0 > 1

Treasure Master

Elemental:
2x Absorption - 2 > 3 > 4
2x Wind - 3 > 4 > 5 (Max)
2x Arcane - 3 > 4 > 5 (Max)
2x Ice - 3 > 4 > 5 (Max)
3x Fire - 3 > 4 > 5 (Max)
3x Thunder - 1 > 2 > 3 > 4

Thunder require a second playthrough so start New Game + and go to the nearest chest to upgrade your last spell.