@Lightning fruit:
Lvl0: Mc can only use a tiny amount of lightning(Because the user is still a Mortal/Non-cultivator)
Lvl1: Mc can use lightning to attack and paralyze his opponent, but not enough to roast them(A strong Beast/Cultivator won't feel anything)
Lvl2: Mc can use the lightning attribute to move faster. (After training enough in this lvl Mc will be able to use GodSpeed) Note: If you don't know Killua or any weird term just Google it :)
Lvl3: User's body will become lightning, immunity to normal attacks and lightning based attacks (Weakened if against a stronger foe), controls over natural lightning.
Lvl4:?Awakening? (The ultimate and final form of a devil fruit)
@String fruit:
Lvl0: Mc can control 1 string, (Dull, but durable, can be used as a rope) can be attached to a solid surface
Lvl1: Mc can control up 5 string, (Still Dull, but good for making traps and taking opponents off guard) Mc can now attach strings to control weaker opponents like puppets.
Lvl2: Mc can use up to 10 razor-sharp strings, (swiping the strings to slice through things like body parts and weapons)
Lvl3: The mc's strings can now be attached to even non-solid surfaces, such as clouds giving the mc the ability of like flight (SkySpiderMan?) and other abilities like compressed strings for various constructs such as ropes usable as whips, bullets, clones, a humongous cage-like force field or a massive spider web defense.
Lvl4:!Awakening!
@Cat fruit:
Lvl0: Gives the mc enhanced smell, sight, hearing etc
Lvl1: Mc will body will transform permanently, (Give the mc a stronger and more durable body, and boost in stamina)
and he can now transform to his first form (Look at the book cover, but imagine a shorter hair (Or just imagine a different haircut) and paler skin, a tiny bit similar to killua) His first form give a boost in strength and a stronger defense.
Lvl2: The mc can transform to his second form, a half-human half Sabertooth(A were-Sabertooth? I need ur opinions on this one!)
Immense strength and defense, Stronger senses and healing factor.
Lvl3: Mc can transform into a giant Sabertooth tiger(Mc become stronger than his Werebeast mode)
Lvl4:$Awakening$
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@Armament:
Lvl0: Mc can cover a first or claw in black metallic armament(As strong as a rock, but not that stronger beast etc can shatter rock easily)
Lvl1: Armament now is as hard as metal, and can cover the entire arm/leg etc.(Still not op, but good for defense)
Lvl2: Mc can Make the armament invisible, and cover more space (He can now cover 2 limbs) Armament is stronger and harder.
Lvl3: User can cover his whole body, and even external objects. (User is as durable as diamond, but note: that this mode consume an insane amount of stamina).
Lvl4:???????
@Observation:
Lvl0: Mc can see things in slow-mo, (But that does not mean he can dodge)
Lvl1: Mc can sense presences 50 meters near him(Invisibility is useless near the mc) Mc can sense auras and emotions (Nothing can hide from the mc, except strong beings)
Lvl2: Mc sense can cover 100 meters, he can see his opponent weakness, (Note that not everyone has weakness in this world) and predict attacks(But can he block them?)
Lvl3: Mc sense is over 200 meters, (He can see more if he focused all his willpower) in this level the mc can even see slightly ahead of the future.
Lvl4:???????!
@Conqueror:
Lvl0: Mc can dominate the weak-willed opponents, making them faint(Can even make an entire army collapse, but mc needs to kill the general to weaken the enemies moral, smart right.😎) range 10 meters.
Mc will get a boost of willpower, (He won't puke his guts out, at the sight of blood, or be overwhelmed by fear anymore) Mc will become fearless.
Note: At this level, Mc can't control his Haki.
Lvl1: Mc conquerors range will become 50 meters, Now he can slightly control haki but he will only knock 50% of the targets, but the stronger ones won't be affected.
Lvl2: Mc now can control his Haki better, (He can knock 100%) in 100 meters range, and slightly weaken the stronger foe, (note that if an opponent had strong willpower he will ignore the effect of the haki) Mc can also use his Haki to intimidate opponents without knocking them out.
Lvl3: Mc has absolute control of haki, (Now he can control who to knock or intimidate)
Mc can knock stronger opponents and create a pressure that can crack buildings
Lvl4:???????