Achievement doesn't pop cause I already have the achievement.
For the Achievement The Works use this method.(time=1-3 minutes)
Start Chapter 6-1(Ship Deck) and make sure you have a flash bang(4-1 has a flash right tat the beginning if you need one) grenade and make sure Sheva has no weapons(so she doesnt kill the Big Majini).
Start the level and go up the first ladder killing anyone in the way(total 6 or 7 enemies). After that go up the second taller ladder and kill the grenade throwing majini(so hes not throwing explosives at you anymore) then jump down and jump down again.
As soon as you hit the ground go right and up the little stairs, this will trigger a cutscene with dogs coming out. Kill the 2 dogs right there(rockets are easiest) and then kill the 2 majini with stun rods(1 will have a worm come out its head) coming from the little stairs.
Then you walk across but before walking across equip the flash grenade. as soon as you go down the stairs straight to your left is the fat majini.
Throw the flash bang at him and then start the chain by pressing "x". Sheva will then quickly attack him right after. Finish up by pressing "x" one more time and you get your achievement.
The reason for using a flash bang is so the big majini won't get hurt and doesn't die before you can land the third attack, which would ultimately not net you the achievement.
RECKLESS x360a thought of this strategy but I found the level making it a lot quicker.
I think I will make a video in a minute.
EDIT: Theres the video sorry no music or anything.