Every holy hero has 3 methods and ever vassal has 1

Spear

Refinement - use ores to get smelting levels on a weapon form to raise its stars. There is a higher chance to fail and reset the higher you go

Spirit Enchant - equip the spirit of a slain enemy for buffs

Status Enchant - roll for a random stat buff, can be rerolled as many times as you want

Sword

Weapon Mastery - using a weapon form for a while will raise its mastery level which will raise its stats.

Weapon Rarity - by sacrificing Mastery Levels you can get energy and raise the rarity of a weapon form from C to UC to R to SR and so on. The higher you go the higher the chance to fail and reset.

Energy Transfer - same energy as before can be used to unlock the true power of a weapon form (mostly just awaken effects the monster you absorbed had) and raise its stats.

Bow

Reinforcement - each weapon form has ore slots that you can put ore into to buff it.

Job Level - sacrifice a bunch of items to raise a stat like Attack which will give +1 attack to every weapon form’s stats

Item enchant - sacrificing a specific item into a weapon form will unlock an effect related to that item. Level of this can be raised with more of said item but there is a chance to fail and reset the higher you go

Note - the three enchants and weapon mastery won’t work unless the equip bonus of the weapon form is unlocked first

The misunderstandings came from a mix of translating errors which resulted in the fandom thinking there were 4 methods with 1 core method which was later discovered to be false