Crazy in love, or maybe just crazy, you've found someone you will do anything for, and have the skills to "protect" them from anything that could threaten your (probably one-sided) relationship. You're aware that in most cases killing for your love is frowned upon, so you've learned to do so from the shadows. Maybe if you just keep killing the competition, Senpai will finally notice you.

Notice Me, Senpai!

Starting at 3rd level, you choose another sentient creature (usually another PC) to designate your "True Love", who you lovingly refer to as your senpai. When you are within 10 feet of him or her, you can use your reaction to subtract 1d4 from any attack roll made towards you or your senpai. The number of dice used for this ability scales with your sneak attack dice, but remains d4s.

You also gain the ability to use your reaction to grant advantage to your senpai's attack rolls and saving throws while in this range, and your senpai can do the same for you.

Obsessive Stalker

At level 3, through stalking your senpai on a daily basis, you have learned to be quick and quiet. You gain proficiency in the Sleight of Hand and Stealth skills. If you already have either of these from another source, you gain the Deception skill instead. Additionally, your base walking speed, as well as any other speeds you have, increases by 10 feet, and you can take a Use an Object action as a bonus action.

Along with all that, your obsession now sustains you, though not entirely. If you begin a long rest with your senpai within 30 feet of you, you only need half as much rest as your race would normally require, as long as you spend the remaining rest time within 30 feet of your senpai watching over them as they sleep.

Unhinged

At 9th level, you sometimes lose control of yourself while fighting for your senpai, bursting into maniacal laughter on the battlefield. As a bonus action, you can laugh maniacally to disturb and frighten your opponents. All creatures hostile to your senpai within a 30- foot radius must make a Wisdom saving throw (DC = 8 + your proficiency bonus + your Charisma modifier) or be frightened for up to a minute. They make additional saves at the end of each of their turns to end this effect. Because you don't want your senpai to think you're crazy, you restrain this ability when they are around. If your senpai is in range of this effect, all creatures affected have advantage on their saves. Once you use this ability, you can't use it again until you complete a short or long rest.

All of Me, All for You

At level 13, your obsession with your senpai has become all-encompassing, to the point where you would literally die for or without them. You gain the following abilities:

• If you are within 10 feet of your senpai and they are targeted with an attack, you can make yourself the target of the attack instead. This does not use a reaction.
• If you or your senpai is the target of a mind-affecting spell or attack, you can end it as an action.
• If your senpai falls unconscious, you let out a bloodcurdling scream. This scream acts like your Unhinged feature, but does not count as a use of Unhinged, and has a range of 60 feet. This scream also grants your senpai one success on a Death Saving throw, as if you had used a medicine check.
• If your senpai fails all three death saving throws or is killed outright by massive damage, you enter a rage of sorts, gaining the following benefits for a number of rounds equal to your Dexterity Modifier:
  • You are under the effects of the Haste Spell.
  • You gain resistance to nonmagical bludgeoning, piercing, and slashing damage. This does stack with other resistances, granting immunity if there would be overlap.
  • You gain one use of a "Suicide Attack". This attack is a guaranteed critical hit, and you apply all sneak attack dice to the damage, regardless of the circumstances of the hit, but your character dies. 
• If your senpai dies and you survive the rage that follows, you have disadvantage on all saving throws and attack rolls after the rage ends until you find a new senpai. When you find a new senpai in this way, your new senpai replaces your old senpai in any memories you have of them.

Endless Love

At level 17, you follow your senpai everywhere. If your senpai starts their turn within 5 feet of you, you can use your reaction to follow them as they move. If they make an attack while within 5 feet of you, you can use your reaction to follow their attack with one of your own, which is made with advantage. If you have already used your reaction to follow your senpai, you can use the same reaction to make the attack.