I think the threat classes need to be explained a bit better.
There are 2 metrics.
1) Monster Class
This is the monster ranking relative to other monsters and how it interacts with human technology.
F - Can be killed by a human in melee.
E - Can be killed by a human armed with a gun.
D - Can barely be killed by a squad of armed humans.
C - Can barely be killed by an army, requires artillery and heavy weapons.
B - Cannot be harmed by human tech, unless it's HERO's monster slaying weapons.
A - Cannot be harmed by anything other than a superhuman.
S - Only level 5s are capable of taking them on.
It seems that nuclear weapons have the capacity to harm even a Rank A, but they will probably do irreversible damage to the planet before taking it down.
Valravn for example is at last a rank B. An army can't kill it.
2) Threat Rank
This is a system HERO uses to determine what superhumans to send after a monster. The Ranks have a +- factor because the sensors are not always capable of painting an accurate picture of the encounter's danger level.
F - One level 1 Superhuman or ignored.
E - One level 1 Superhuman
D - Two level 1 Superhumans
C - One level 1 & One level 2 Superhumans
B - Level 3 Superhumans or higher only.
A - Level 4 Superhumans or higher only.
S - Special encounters for level 5s.
The Rank system is based on safety and generally HERO send their agents in pairs to avoid a miscalculated threat Rank. The teacher claims that a level 2 is generally capable of handling a C, but he may have trouble handling a C+, which is why they send agends in pairs.
Valravn is Rank B because according to HERO logic, a level 2 has almost non existing chances of beating that encounter. (And frankly this is true, Valravn has enough power to cut through any level 2 and kill them on the spot. MC regenerates and is squishy as fuck so all this power goes wasted).
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MC has punched above his weight class 2 times after joining HERO.
1) He beat Valravn, B Class/B Rank as a level 2 when HERO only send level 3s to deal with them. Valravn was not at full power at the time, but his power levels seem to be unsually malleable. I have hypothesized that he is in fact an S rank at full power.
2) He beat the Asura, A Class/A(-) Rank as a level 3, when HERO only send level 4s to deal with them. Asura was injured from a previous fight and already had a wound that MC could exploit. Additionally he had a visual impairment due to Nico summoning lava directly on his head and reaching it's eyes.
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My opinion on various monster rank and threat class:
Minyak - Rank D+ | Class D
Minyaks have some trickery that may be too dangerous for a single level 2. The authority part of their abilities along with the fusion.
Light Monster - Rank D+ | Class D
This monster while fairly weak, it's particularly dangerous because it can pretty much immobilize it's prey.
Chimera (Michael) - Rank D | Class D
While it has a lot of abilities, it can easily be harmed by human tech. Michael fought it mostly without his abilities, but once he unlocked them it was childs play for him. Still fairly dangerous for a level 1, but Michael punches above his weight class.
Chimera (Alice) - Rank C+ | Class C
This thing was way more dangerous than Michael's Chimera. It completely outclassed Laurie because it had many ways to deal with her power, and the level 1 Alice who is fairly good at offense, couldn't harm it.
Deryl (Hydra) - Rank C+ | Class C
It's hard for me to rate Deryl has Rank B, although tbh. It's powers while versatile, they are tailored to MC's weaknesses. Deryl would be fairly weak against someone who is better at range for example, and it's fairly easy to formulate a human strategy to deal with him, consisting of heavy artillery and air attacks. Valravn would just kill him instantly, Level 3 MC would just pierce all his heads with his tail without even thinking. However that + here is significant for MC.
Deryl (Monster) - Rank B+ | Class B
Yeah, that thing is certainly not a normal Rank B. Extemely tough, huge enough for most attacks to not make it far inside it's skin, with regeneration and a myriad different attacks, including a hydrogen cannon that can vaporize mountains. Valravn was a normal rank B and a level 3 MC would beat him to a pulp no problem.
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A small observation on MC's offense:
MC is mostly a defensive/technical superhuman. However some of the fights really showcase his offensive capacity. As a level 2 he can deal significantly more damage than whatever humans can do without nuclear bombs. At level 3 he has enough offense to beat an A Class monster and enough defense to withstands it's attacks.
A level 3 MC, despite not being offensively oriented, has more offense than anything in the mundane world and monster tech, something that HERO seem to attribute to level 4 superhumans based on the class descriptions. He still lacks power, but considering that the Asura was about 10 times stronger than him according to the narration, with the current rate of improvement of about 15-20 power per week, in about 3 years he should be able to make short work of A class monsters even without evolving, and that's without introducing any more monster physical abilities to his attacks.
I attribute this to his memory ability. Up till level 2 MC was fairly squishy. Even bullets could hurt him. Once he created his plate armor, he has become almost invincible. Additionally the 2 attacks that obliterated Deryl were based on monster memories and mechanics.
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Could MC beat the Asura in full strength?
Technically yes but HIGHLY unlikely. The blinded Asura managed to get him. If it had it's vision, it would be very hard to dodge it's attacks. Perhaps with Nico's portals he could do it, but still, while he has the power and defense to beat it, he is just not there yet.
Thoughts?