Soulcalibur IV

I think the best way to get this achievement is to use Yun-Seong.

Simply go into story mode and spam his Forward+Y+Y attack which the oppopnent will almost definately block. When you see red lightning around their character press LB.

To make this even easier level Yun-Seong to level 9, then give him low attack and skills such as Soul Gague Vamp and Soul Gague Damage A.

In story mode you should get be able to critical finish every opponent, which will give you around 10 more critical finishes towards this achievement.

This achievement is very easy to do on floors 3-4 in the Tower Of Lost Souls. Use Soul Gauge Damage A, Yun-Seong Style, and keep doing the Forward-Y-Y (if you get the rhythm wrong, then the enemie will be broken then he/she'll continue. So be careful.), or just Yun-Seong no-edits (They both work). You will get 4 or 5 per run-through (I say or because sometimes your just unlucky) That would be only 20-25 times, and you probably have done it a few times anyway during normal fights :)
A Yun-Seong with low attack, Soul Gauge Damage A, and high defense is the best, and will get it on almost every battle you go into, even characters with Auto Impact :)

There's a really simple way to boost this with a friend. Go ahead and set up an Online Special Versus Player Match. Whoever wishes to work on Critical Finishes should create the following Yun-Seong (credit goes out to Fatboyy for a nearly identical Yun-Seong, minus the Sorghum and some skills):

Weapon: Sorghum
Head: Horns of Calamity
Face: Usurper's Mask
Neck: Juok Chaplet
Shoulder: Paladin's Pauldrons
Undergarments: Executioner's Fauld
Upper Body: Noble Garment
Arm: Vagrant's Kote
Lower Body: Samurai's Hakama
Ankle: Shinobi Tabi
Leg: Hero's Shoes
Skill 1: Soul Gauge Damage A (recommended)
Skill 2: Start Dash B (personal)
Skill 3: Nullify Ring Out C (personal)
Skill 4: N/A

While one person is working on Critical Finishes, the other player should select Ivy, since she defaults with Auto Impact A and can simultaneously work on "Like a Flowing Stream". If the other person already has this achievement, character does not matter.

The match settings don't particularly matter; with 1 round, you can quickly work towards getting "Engraved into History", whereas with multiple rounds, you can get more Impacts, Soul Crushes, and Critical Finishes with less loading time. I recommend the level Phantom Pavilion due to having four walls, preventing ring outs.

Have the other player (Ivy if working on Impacts, anybody if not) continuously guard while Yun-Seong uses his X+X combo (against Ivy for Impacts) or his Forward+Y move. Eventually, the guarding player will have a flashing red meter. At this point, disregard the X+X combo for Impacts and use Forward+Y for sure. After two or three hits, you will obtain a Soul Crush. I highly recommend capitalizing and pressing LB to perform a Critical Finish.

An easier method of getting this is to create a character that has the ability Soul gauge damage A (I would advise using a Nightmare model meaning you can use his left and X move repeatedly). Now go to tower of lost souls and go to floors 3 to 4. On this floor the opponents block often making this achievment a lot easier. Just remember to only use single attacks when their soul gauge is flashing red and to press LB as soon as you see the red flash around their character.

OK, so the other guides weren't really helping me as I never really understood what I was supposed to do and when, so I figured I'd write a solution.

First, make sure your controls are set to "Type A". If you're not sure if you've modified them, reset them in the Options/Control Options menu. Of course, if you're good with your control scheme and know what to press for Critical Finishes, do what you like! This solution assumes LB will be used.

Next, I customized Yun-Seong, using a slightly lower power build than the others I've seen. It was plenty for what I needed:

Hero's Band
Monocle (Right Eye)
Dueler's Necklace
Paladin's Pauldrons
Executioner's Fauld
Noble Garment
Vagrant's Kote
Paladin's Fauld
Shinobi Tabi
Hero's Shoes

Weapon: Sorghum

Skills: Soul Gauge Damage A, Nullify Ring Out C

Then go to Single Player Modes/Tower of the Lost Souls/Ascend/11F.

So what to actually do: The combo is toward+Y+Y. That's hold toward the enemy, then press Y, Y in a paced attack so that your character does two large, sweeping attacks. You want the enemy to block these (you can't control this) and for the red orb at the end of their health bar to eventually turn red.

At this point, you're looking for a soul crush to happen - that's when a red lightning coloration occurs and a piece of enemy equipment is broken. It appears that exactly SEVEN (7) blocked toward+Y attacks will generate a soul crush on the enemies on Floor 11. (If you lose your streak and it takes a while to hit the enemy again, you might see this rise to 8, 9, etc. hits total.) When that happens, you want to quickly press LB before any other attacks, and your character will do its Critical Finish, instantly defeating the enemy. Repeat for the rest of the enemies and you'll have up to 4 Critical Finishes per match.

Naturally, since you're pressing toward+Y+Y, you may get the soul crush on the first hit of the two-hit combo and so the second hit will ruin this. I found that slowing down and doing single toward+Y hits were unreliable, as the enemy seemed less inclined to block. No matter. Just start charging up the soul crush again, and try again.

I didn't worry about positioning at all - just attack, attack, attack. Eventually I got into a rhythm where I got Critical Finishes on all enemies most times, some on second or even third soul crush, but most on my first. I was able to count the 7 blocks and time it pretty well, but at first you might just have to experiment to find your own rhythm.

I hope this helps. I'm not a fighting game enthusiast so I wanted to provide some tips for those of us who find all of this stuff less intuitive than others do.