I don't understand the weapon upgrade system

[Chrisern]

Why are some weapons greyed out, and how do I get access to them? Do I need to make weapons lower on the tree to get access to just that branch, or how does this work? Do I need recepies? Is it a waste of rescources to upgrade lower tier weapons? When can I see the whole tree? Is it linked to HR?

[AllergicToBrainRot]

you need to hunt said monsters to unlock said weapon upgrades. Keep doing the main quests to unlock more monsters to hunt or capture to unlock more weapons and armors, ect.

[JPM岩]

As you hunt monsters, youll unlock more trees, or at least being able to see more trees. As you progress and increase your HR, youll have access to more upgrades for said trees. Youll see the whole tree when you've killed every monster once, and clear the story.

[AurumHawke]

Forging a new weapon instead of upgrading to it has a different material cost, usually more of the specific monster or even a rare material.
Weapons can be downgraded to recover the specified materials, but the pick-your-own-cost points materials can't be recovered.
So it usually costs more, but more plentiful, materials to upgrade to something you can forge. It depends on what you have on-hand.
And some branches can't be forged, and some upgrades prevent rollback.

Each tier (left-to-right) is unlocked by progressing your rank (by the quest star system).
Each branch (top-to-bottom) is unlocked by fighting the monster and further tiers of that branch by getting that upgrade's key material.
Quest and Event reward weapons are unlocked by completing the side-quest or getting the event material(s).
So the entire tree should be unlocked at post-game once you've completed every side-quest and acquired at least one of every material.

[Emerald Lance]

It is worth upgrading your weapons because the same weapons continue to get stronger in high rank; low rank armor is not worth investing in since it does not become high rank armor later, and new high rank armor will need to be reforged from scratch whenever you get to high rank.

Weapons are greyed out when you lack the materials to make them. Iirc, you need to have at least half of the material types for the weapon's requirements to be revealed.

Most of the time you will need to start a brand new weapon from bone or iron or whatever in order to craft it up into the weapon you will want. There are exceptions though, and you can generally craft new weapons further along the different trees at "checkpoint" intervals. It's difficult to explain in words, honestly.

[Tymon]

I mean, technically it isn't even actually an 'upgrade' as the upgrade turns into an entirely new weapon. In some cases, not even a direct upgrade to the previous item as it is a completely different element/effects/etc. So I can see why it would be confusing...