You create a sword-shaped plane of force that hovers within range. It lasts for the duration.

When the sword appears, you make a melee spell attack against a target of your choice within 5 feet of the sword. On a hit, the target takes force damage equal to 4d10 plus your spellcasting ability modifier. Until the spell ends, you can use a bonus action on each of your turns to move the sword up to 40 feet to a spot you can see and repeat this attack against the same target or a different one. 

When you make a melee attack with this sword, you can target up to three creatures as long as they are within 5 feet of each other. 

The sword can attack creatures on the Ethereal Plane.  You can see Etheral creatures as long as they are within 10 feet of the sword.  It counts as a solid object on the Ethereal Plane, impeding ethereal travel.  

While the sword is summoned and is within 120 feet of you, you can use an action to destroy the sword.  The sword bursts into an explosion of Ethereal energy.  Each creature within 30 feet of the sword's space must make a Dexterity saving throw, taking 6d8 force damage on a failed save, or half as much damage on a successful one.  On a failed save, a creature is stunned until the end of your next turn.  The explosion leaves behind a sphere of force in the space of the explosion.  Nothing can physically pass through the sphere, and the sphere also blocks Ethereal travel.  Spell effects can target location or creatures on the other side of the sphere, with the exception of spell attack rolls.  Area of effect abilities don't extend through the sphere.  The sphere is transparent.    

At Higher Levels.  When you cast this spell using an 8th-level spell slot or higher, the sword may target two additional creatures (within the same range) for each spell slot level above 7th.