A warrior stands on a bridge between a defenseless town and a evil warband of goblins, as the ugly savages charge he grips his trusty longsword the only weapon he carries. Like lightning he begins to slash goblins in half as though he was a god of war. Afterwards the villagers are somewhat bothered out how their "hero" now sits in the tavern converse with the same blade and telling it how trusty it is. 

A half elf readies her bow, seeing the ogres throwing her unconscious friends into a wooden bow so as they argue who they eat first. As she pulls the string back the environment around her almost seems to bend and twist giving her the perfect shot into the ear of all three of the dim-witted brutes. Before releasing the arrow she seems to thank the bow.

The hobgoblins all begin to mock the simpleton goliath who has walked into there camp. But this goliath came seeking vengeance for the innocent people they slaughtered. As the red goblinoids continue to laugh and begin to surround him brandishing swords and axes those laughs turn to silent expressions of fear as the giant reaches both hands out summoning a glaive. Now he laughs as tells his weapon how these hobgoblins now face the justice of what they've done to it. 

While many fighters can wield almost any weapon The Weapon Masters pride themselves for creating a unique bond with one weapon that makes them especially lethal and seemingly mad to those around them. 

Spirit of the Weapon

Your weapon seems to have a being tethered to it. This being's existence is only noticeable to you while not actively using your weapon to attack. While it's in its humanoid form it can give you advantage on any "mental" ability check (ie perception, investigation, etc.) You can do this amount of times equal to your INT modifier per short rest.

Weapon of Choice

You have trained not only in the conventional use of your weapon but also have created your own style of combat with it. Your weapon gains an additional weapon property as well as a mystic property. You gain an additional weapon property and mystic property at level 10, 15, and 20. 

Weapon Properties:

Versatility- Your weapon can be wielded with one or two hands. If your weapon was only two handed before the one handed damage die is one die less than the two handed and vice versa for a one handed weapon. (ie Versatile great sword dealing 2d4 damage one handed)

Thrown- Your weapon is now throwable. Versatile weapons can be thrown one or two handed the range of this weapon is 30/90 feet 

Finesse- Your weapon can be wielded with STR or DEX.

Reach- Your weapon's reach is extended by 5 feet. 

Mystical Properties:

Elemental Bane- Once per turn your weapon deals an extra 1d6 is one of the following types: cold, fire, acid, poison.

Magic Vessel- Your weapon becomes magical gaining a plus 1 to attack and damage rolls. It also can be used as a spell focus if you can cast spells.

Reliant Wrecker- Your weapon comes flying to your hand when you summon it. This works as long as you are both on the same plane of existence any object or creature attempting to stop your weapon must make a STR check = 10+ proficiency bonus+ INT modifier (either losing grip on it or getting pulled to you as well if they managed to hang on DM discretion). Your weapon can be summoned free of action once per turn. 

Merciless Weapon- Your attacks deal an extra 1d4 of necrotic damage to any creature below its maximum hitpoints.

Titans Tool- Your weapon becomes "oversized" and does an additional damage die of damage on every hit but becomes nearly impossible to hide and takes up half your carrying capacity. Any creature except yourself attempting to lift it must succeed a STR check of 8 + twice its original weight. (Must at least have a strength of 18 to pick this property)

Damage Deal- Once per turn whenever you make a successful attack your weapon harnesses the power of that attack. You can choose to either gain hitpoints equal to half the damge dealt or you gain half the damage dealt as bonus on your next attack. 

The Only Tool I Need...

At level 7 your weapon can also assist you out of battle, any ability check that you can use your weapon to assist you on gains a bonus equal to 1d4+ your INT modifier (min of 0). 

(ie using your weapon to Intimidate someone or showing off your weapon and skills as a performance check)

Student of War

Upon reaching level 10 you can channel all your training and focus to become a near unstoppable warrior. Once per day you can add your INT mod to all intuitive, attack, and damage rolls (min of 1) you also add that bonus on any ability check that you are proficient in. This state last for 10 minutes but you must be carrying your special weapon and the combat bonuses apply only if you attack with that weapon.

Weapon of The Master

At level 15 your weapon has a supernatural bond with you. As if it were sentient it refuses to be wielded by any other creature no matter alignment or if they are someone you know. Any creature attempting to make an attack with your weapon automatically fails and the damage that would've been dealt is dealt to them instead. 

Your Best Ally

Your weapon can gain a humanoid form that was previously only known and seen by you but know all creatures can see it. Previously this "ally" of yours was only visible and could only interact with you directly but now you can give it true physical form allowing it to interact with its environment as if it were a real person. This last a number of hours equal to your INT mod and can not be a part of combat unless in weapon form.