SevenKey

SevenKey is a thing.
Michael K. Barron is a teenager with underdeveloped emotions as a result of severe depression. Unbeknownst to him, this allows him to wield a device called the KeyTrix, originally designed to corrupt its user with the vices of the Seven Deadly Sins, without repercussion.
This remains unknown until a particularly determined commander of the forces trying to invade Earth realizes what's going on and dies reporting it to command. He notes specifically during his battle with Michael, "All this time, we though we were fighting some invincible super-soldier with an iron will beyond any mortal comprehension. But you're not strong at all. You're just empty.". The creator of the KeyTrix takes advantage of this by forcibly activating the DeadKey forms, which are incredibly powerful, dangerous versions of the KeyTrix's base forms that take on their own willpower instead of just corrupting the user's existing one.
This is initially debilitating, as Michael's lack of his own willpower leaves him unable to control the DeadKey forms. He eventually learns to create something to hold onto, even if it's vague, and uses that to "artificially" give himself enough willpower to contain and control the DeadKey forms. Unfortunately, this leaves him open to corruption by the standard forms, which slowly deteriorate his already poor mental health.
At his lowest point, Michael has an epiphany about the vices controlling him and the reason they exist in humanity in the first place. He learns to embrace these faults and turn them around into positive factors, creating the Virtuous forms, something even the KeyTrix creator didn't think was possible (which it was since the KeyTrix is powered by the user's Ki, the creator just hadn't considered the idea of someone actually turning the vices on their heads as a possibility).
Eventually the war is won and Michael moves on with his life with a newfound sense of "eh maybe i should live for a little while and see what happens". Series ends. Bada bing bada boom.
== Aliens ==
# Pride - ???: A shiny crystal alien.
# Greed
# Lust - Feel Good Inc: I mean duh
# Wrath - SteamBriner: A fire/water alien.
# Envy
# Gluttony - ???: An alien covered in mouths that grows as it eats.
# Sloth - ???: An alien that stops time. Though the alien retains all consciousness in stopped time, it takes extreme willpower from the user to move in stopped time. Michael has incredible difficulty controlling this one because of his depression.