Onimusha: Warlords

You can complete this game with 3 play-throughs (2 if you really want to).

Playthrough 1
Play on Normal. Get all the collectables and in particular, all 20 fluorite. Also, make sure you get the bishumon sword.

After completing the game with all 20 fluorite a mini-game called "Oni Spirits will become available. Complete this game and you will be able to take the bishumon sword + infinite magic into the "ulitimate difficulty."

Playthrough 2
Play on ultimate difficulty. This will be a joke with the infinite magic, arrows, bullets and the big sword. Use this chance to get the S ranking. Make sure you create a save point just before using the arrow to enter the underworld. If you finish the game with less than the 500 required kills, go back and farm the "dark realm". Again an S rank is 500 kills, 50,000 souls and less than 3 hours.

If you are wondering if you can knock out no herbs, jewels etc during this fun run... the answer is no. The other achievements do not stack with this difficulty.

Playthrough 3
Play on normal again but this time do not use herbs/medicine or do not upgrade the swords or use any jewels. You can and are required to upgrade ability to open doors. However, still collect all the herbs, medicines, bullets, arrows and jewels that you come across. I will explain.

Save often. The big challenge here are the parts with the female ninja. You play 3 times with her. The first time will be with puzzles and she really cant take damage. The second and third times, make sure you are mindful of her health as she can not regenerate. Make sure you leave her with at least 50% health for the third and final run with her.

The hard part are the final 2 bosses. But here is where we make things easy. Create a save right before you enter the underworld using the bow and arrow.

With the save point created you can now break one set of rules and then reload the save and then break the other:
1. Finish the last 2 bosses using herbs or medicine. I collected about 23 herb/medicines. You can enhance all herbs to medicine if you want. You may want to convert some bullets to blast bullets too. Complete the game~just dont upgrade swords or use jewels.
2. Upgrade all swords and use all the jewels. I had around 50,000 souls and was able to upgrade all swords and most of my arrows and bullets. Complete the game~just dont use any herbs/medicine.

Talisman and soul absorber- these can be helpful in the final battles and do not count against the achievement. The talisman can be found in the east area on a small island to the south that will require you to shoot an arrow to extend a bridge. The other can be farmed in the dark realm on wave 15(not really worth the effort). The soul absorber can be used to release the souls of any enemy that will give you health/magic when you need it.

If you are having any problems with the bosses:
Giant bee woman-use up all magic in this combination order wind, fire lightning. Then use burst bullets.
Marcell- Use up all your magic until he is in second form. Then use burst bullets. Should take about 12 shots.
Fortinbras- This time lightning followed by a fire when his head is low. Grab the magic orb and use wind to block when pulling in the magic orb. When he uses the fire breath stand in either corner and fire flame arrows. If you are out of magic, spamming the flame arrows while dodging attacks works OK you are able to get another orb.

Complete Oni Spirits mini-game once, afterwards Ultimate difficulty will be unlocked from the start menu, then simply play through the game on this difficulty