Nilisnebar, the Amber Xiphos

A translucent leaf-shaped blade made from a single crystal of amber. The hilt is made from bronze, with an ornate circular guard set with a large polished amber sphere. The blade carries an inscription in elvish: nilisnebar - Nilisnebar, 'Storm-Glass (Amber) Blade'. Magic swirls throughout the crystalline blade, and sometimes small jolts of lightning can be seen inside the amber.

Nilisnebar was wielded by Aerilwyn Nilteril, a legendary bladesinger who served the Teccan Empire at its height of power.

Sentience. Aerilwyn's very essence has infused into Nilisnebar, making it sentient. It is Lawful Neutral and has an Intelligence of 22, a Wisdom of 16, and a Charisma of 15. It has darkvision with a range of 60 feet and communicates telepathically with the wielder, preferring to speak Elvish but will speak Common if needed. An attuned creature can respond telepathically.

Dormant

• You gain a +1 bonus to attack and damage rolls made with this magic weapon, which can be used as a spellcasting focus.
• The weapon has 10 charges. The sword recharges 1d6+4 charges on a long rest. You can use the charges to cast the following spells: Shatter (2 charges), Thunder Step (3 charges). The spells use your spell save DC.
• After you attack with Nilisnebar, you can cast a spell using a spell slot with a casting time of one action as a bonus action until the end of your turn by spending 5 of its charges.

Awakened

• The sword's bonus to attack and damage rolls increases to +2.
• You can use your spellcasting modifier instead of Strength or Dexterity for the attack and damage rolls with this sword. If you can make multiple attacks, you can replace one of those attacks with a cantrip that uses your weapon.
• You have resistance to lightning and thunder damage.
• The number of charges increases to 15, and the charges restored on a long rest increases to 1d10+5. In addition, you can cast Lightning Bolt by spending 5 charges.

Exalted

• The sword's bonus to attack and damage rolls increases to +3 and when you hit with it the target takes an extra 1d6 lightning damage.
• If you use this sword as the material component to cast a cantrip, you have advantage on the attack.
• You have immunity to lightning and thunder damage.
• The number of charges increases to 20, and the charges restored on a long rest increases to 1d12+8. In addition, you can cast Chain Lightning by spending 10 charges.

Personality. Aerilwyn is very intelligent, calculating, and hungry for power. She knows much about magic and the history of the Teccan Empire, and will share these facts with wielders she considers worthy of continuing her legacy. A worthy wielder of Nilisnebar, in her view, is someone who is an accomplished arcane caster with ambitions (especially political or pertaining to an organization) and the drive to accomplish them. If the wielder is not worthy, she will try to guide them toward this path. Aerilwyn enjoys seeing evil destroyed by magic, especially lightning magic. Aerilwyn is still loyal to the Teccan Empire, and is shocked upon hearing of its fall. Her ultimate ambition would be to revive the empire, installing a worthy emperor once again.

As the wielder grows closer with the blade, Aerilwyn will grant them more of the sword's powers. This should occur at major plot points when the wielder takes steps towards becoming a 'second Aerilwyn', such as getting promoted into command of a military unit, defeating a powerful foe, or discovering a long-sought piece of arcane research. The sword might also unleash its power in dire circumstances if Aerilwyn finds the wielder worthy of her protection.