For the most part you will be working on this right from the very start of the game.
Before you forge the Armageddon blade, youll want to do this (as it replaces your Chaoseater and wont be able to work on this weapon).
NOTE : Supposedly Choaseater does not need to be upgraded according to the comment. Keep in mind, i wrote this guide as i was playing, and any edits that were in this guide were lost in the great TA crash/losing of data.
Please also note the Choaseater listed below is a recommendation not a MUST use.
First up -
Chaoseater - Fury's Embrace
Scythe - Death's Blessings
Tremor Gauntlet - War's Glory
Second -Where to find
War's Glory - Legendary - improves chaos regen and weapon
After you fight the first large crystal/hungry spider youll come to a passage with 1 shadowflight blue orb and lots of abyssal chain orbs, jump into the shadow flight orb and pull back on the stick for a secret ledge and the Legendary weapon mod
Fury's Embrace - Legendary - reveals all items on maps
Enter black throne, head east, past the outside area.
When you get to the 2 button on opposite end of a chasm that produce a rock pieces brigge do the following.
Have void walker item ready, activate bridge, as your moving across, you need to look up and to the left and fire a shot at the void design. Once over the other side of the bridge, hit the button and make your way back to the void design. Use void, walk through void, press button and cross another collapseable rock bridge to recieve this Legendary weapon mod.
Blood Thirst - Leeches health when damaging enemies
Enter the twilight catherdral, cross the lava and go right through the door, drop down hole in this courtyard. Follow to end open door, turn left, go straight ahead, keep heading west. Take elevator down, in this room there are 2 lit sconces and 1 unlit, use crossblade to light the one to get your chest.
Strife's Offering - Legendary increase gun effectiveness
Ashlands, jump down the drill hole, follow until you come to the section with 12 plant teeth hanging from the ceiling. Go towards and use the shadowflight orb, then Abyssal chain across. After killing everything receive your reward.
Death's Blessing - Legendary -
Head north out of Scalding Gallows, youll come to the huge door that requires the Chrono puzzle to get past.
Place a void on the void design.
Activate the chronomancer the switch and make it past the big gate.
Once the gate crashed down look at it, place the other powered up void hole on it.
Activate the switch and run back to the chronomancer puzzle room.
Activate the switch, look through the void till you see the chest then jump through for the weapon enhancement.
Third - Why these enhancements,
Having all these slotted seem to stack, when using the weapon with these slotted i always gained health back, even though the weapon i killed with didnt have a leech ability.
The time it took me to level the last half bar with the Scythe using Death's Blessing, and the last half bar with the Tremor Gauntlet using War's Glory were.
Scythe+Death's = 1/2 bar = 15minutes
Tremour+War's = 1/2 bar = 15minutes
I did 1 1/2 levels on the Tremor gauntlet, and 3/4 a level on the Scythe and clocked up approximately 12000 souls.
This will help if you need extra souls to purchase the weapon abilities.
Fourth - Purchaseable items.
These are all the Chaoseater/Scythe/Tremor Gauntlet moves.
You do not have to purchase any the equipment(Crossblade/Mercy) upgrades.
Fifth - Best moves to use.
Sword - 180 orbital, (X pause X) or hit X,X, then wait a moment and repeat.
after you round them up, Hit Y,Y then wait a moment and repeat.
Or the push foward and hold RB+Y (this will so a sliding swing attack)
Stand still and press RB+Y, this will do a ground slam and pummel.
Sixth - Equipment
Pull stragglers toward you to finish them off, but not a necessary piece of equipment.
Seveth - Location, Location, Location
After defeating Silithia(or before it, its just easier to describe the location working backwards).
Leave the Silithia room and go back the way you came,(this is web door number 1). Work your way back and go through webdoor number 2..
Take a left and head down the hole, this next room has a load of spiders on the wall.
Round them all up and use your ability.
Now here is the trick to reseting this room.
After you have cleared out the room, climb back up the growth, dash forward 3 times, this will put you on a non-concrete floor. (This is the reset area - tested to see if this could be done any closer and it couldn't.)
Turn around and go back into the room all spiders respawned.
Once you have all the moves and the weapons upgraded, and have collected all the Armageddon blade pieces. Go get your Armageddon Blade recrafted once the cutscene is done, you will receive this achievement.
If you formed the Armageddon blade before you bought the last pieces from Vulgrim, the achievement should pop once you exit Vulgrim's store.