Hades

After you unlock all the weapons, you will get the option to reveal different 4 aspects for each weapon. They give bonus stats, and some have slightly different move sets.

Right away you’ll have access to 3, the base aspect, and 2 other aspects that can be purchased for Titan blood. The last aspect on each is hidden. Unlocking it comes down to performing different tasks that prompt dialogues with the right characters, who give you a phrase to unlock the aspect. These conversations are more or less random, and some need certain triggers.

The unlocks are:

-Guan Yu (spear): trigger a certain dialogue with Achilles. This conversation is random, so make sure you talk to Achilles on the west wing after every run. He’ll mention it in a conversation, and you can run into your weapon room to reveal the aspect

-Aspect of Arthur (sword): like Guan Yu, Arthur is unlocked by having enough conversations with Nyx that she mentions it. Make sure you talk to her whenever you can after a run, and eventually she’ll give Zagreus the phrase

-Aspect of Gilgamesh (fists): unlocked by running into the Minotaur miniboss in Elysium WHILE the fists are equipped. This one can be very RNG, as there’s no guarantee if you even make it to elysium that you’ll fight Asterius as the miniboss. The final boss room with Theseus doesn’t count, so keep using the fists and picking doors that have the skull icon under their reward (these indicate minibosses/challenge rooms)

-Aspect of Beowulf (shield): given to you by talking to Chaos. Throughout runs you’ll a multicolor eye panel on the floor. After clearing the room inside, you can go in the now open portal for health. Inside these you can talk to chaos. Like Achilles and Nyx, he (they?) will eventually give you the phrase to activate this aspect.

-Aspect of Lucifer (gun): given by talking to Zeus. After picking up so many of his boons during runs, he will mention the weapon and give you the phrase, much like the rest of them

-Aspect of Rama (bow): like the others, it’s given by having enough dialogues with Artemis. Eventually she will give you the phrase to unlock this for the bow

With that in mind, after you unlock these, simply clear a run with one of them equipped.

If you’re finding it hard you can try:
-setting the pact of punishment to 0 heat (even if you’ve already cleared a run at this level with the weapon)
-a different hidden aspect
-gaining more darkness upgrades
-upgrading the hidden aspect with Titan blood

If you want a more detailed guide on clearing a run, check out the guide for “Is There No Escape?”