Soulcalibur IV

Customize Mitsurugi to have Auto Impact A and Impact Heal. Go into his Story Mode. The first opponent, Setsuka, tends to use mostly high and medium attacks, so just stand there and guard the whole time.

I found a method to get this one in no time. The best I've gotten was 61 impacts/match, but even more is possible.

I used a custom Mitsurugi with impact heal, high def and high GP (health) and low attack (you don't need impact heal but it helps). Go to TOLS stage 11. The first enemy is Ayala (or Araya?).
Now you do the following: Just keep hitting her with the X-attack. If she blocks (and she'll block a lot), she'll try to hit you right after your attack. So after being blocked hit 6G (forward+guard) and you should get an impact. If she ducks, you'll miss your hit, but she'll most likely do a WR attack afterwards, that means another easy-to-see impact for you.

This worked great for me, I needed 92 impacts and I got them in two matches. Often I got 4 or more impacts in a row. If you defeat the first opponent in stage 11 TOLS, the next one is a Cervantes style char, but it is the same here. Let him block your X-attack, and 6G right after being blocked.

Shouldn't take longer than 30min to get the achievement.

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 knock out the Impacts first should select Ivy, since her default character already has Auto Impact A, while the other player selects the customized Yun-Seong I recommend in my "Mad Destroyer" and "Death on the Battlefield" solutions. If you're too lazy to look at those solutions, create this 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

With this Yun-Seong, the player that is not using Ivy for Impacts can work on Soul Crushes and Critical Finishes at the same time.

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.

Simply guard with Ivy while Yun-Seong attacks high with his X+X combo. You should get anywhere from 5 to 15 Impacts per round, depending on how lucky you are.