Dynasty Warriors 7

There are 13 Guardian animals that must be obtained in Conquest mode to get this achievement, 10 can be bought from the Merchant, one at a time, who will appear in the cities after every 2-5 battles and will slowly in price up to 20,000 gold. The other 3 can be obtained as a prize for winning certain stages on the map (Pictured below in the black tiles)

The animals are:
Mahogany
Birch
Chestnut
Maple
Shadow Runner
Hex Mark
Red Hare
Elephant
Tiger
Wolf
Panda
Bear
Falcon

In order to get this achievement, you'll need to acquire all the guardian animals. Most of these are bought from the merchant that is occasionally in town. You can only buy one of them from the merchant at a time, and after you check what he has for sale he disappears until you fight a few battles (usually ~5).

3 have to be unlocked by finishing certain battles. These battles are tiles on the map that have an animal's face on them (a tiger's?). They are all fairly hard, so you'll need a somewhat powered up officer with a decent weapon.