While making your way through Onimusha: Warlords, you're likely to encounter items known as Magic Jewels and Power Jewels. These are pick ups that permanently upgrade both your health and magic metres, and so naturally you're going to want to find as many as possible. In doing so, you will also unlock two Bronze Trophies named 'Demonic Vitality' and 'Magic Overload'. Here's where you can locate every single one of them.
All Magic Jewel Locations in Onimusha: Warlords
After leaving the Underground Temple via the moving statue, look to Samanosuke's immediate right. There will be a chest hidden there amongst the foliage containing the Magic Jewel.
Once you reach the second floor of the Keep, you'll need to rescue two allied soldiers before the undead enemies reach them. Take them out without suffering any casualties and one of the two soldiers will drop a Magic Jewel for you.
In the West Area, you'll find a chest just before the door that requires the Gold and Silver Plates. Solve the Chest Test and the Magic Jewel is yours.
When you reach the East Area, you'll encounter a very large building that you need to enter. Reach the top of the structure and open a chest next to the ladder to claim the next Magic Jewel.
As soon as you see a waterfall, you're going to want to enter the house found next to it. Once again solve the Chest Test found inside and you'll get your hands on the final Magic Jewel.
All Power Jewel Locations in Onimusha: Warlords
Found just after the first Magic Jewel, you'll pick up the first Power Jewel from a Chest Test located beside the next save point you come across.
Just before the first boss encounter, there'll be a Chest Test for you to solve next to a save point. Crack the puzzle and another Power Jewel is yours.
On the third floor of the Keep, enter the door on Samanosuke's right once you've climbed the stairs. Inside there, examine the Hanging Bucket and you'll discover another Power Jewel to add to your arsenal. Make sure you don't take a swing at the rope holding it up though, otherwise you won't be able to pick the upgrade up until later on in the game.
Once again in the Keep, you'll need to gain access to the secret passage behind the strategy room where you'll find a chest containing the penultimate Power Jewel.
Remember the huge building in the East Area where you found a Magic Jewel? There's also a Power Jewel there to be picked up, found near a dead body on the rooftop.