To explain how this test works and what happened:
This test, like the preliminary test, has a pretty lax minimum pass requirement but opportunities to gain extra credit. This is part of the overall testing procedure to measure how determined you are. If you keep passing with the lowest effort possible, the proctors will not look on you favorably. You are intended to score as high as possible on each step.
The doors are meant to be opened with your mana. The more mana you have, the more doors you can open. Haerang opened the first couple of doors with just pure muscle power and that wasn't supposed to happen. I remember the WN made a big deal out of it. Remember this for Kyunwoo.
In this chapter we also see Haneul's Gift translated as Splitting. The nature of this was revealed very early in the WN (like chapter 1) so it's not a big spoiler to reveal that it is literally Shadow Clone Jutsu. I mean literally. In Haneul's bad ending, she infinitely multiplies enough to destroy all life on the planet before turning on herself. Her massive mana pool allowed her to easily open all 5 gates.
Kyunwoo's comparatively smaller mana pool doesn't. However, he did not cheat to open 5 gates and the detail will probably be revealed next chapter. The gist of it is Evasion Instinct bailed him out and next chapter we'll probably see the proctors complain about cheating but Yena covers for him with some bullshit about cleverly utilizing Light and Dark Mana explosion to blow open the door. She even has them check the gates for malfunctions and they're given the all clear. However, she privately wonders if he was stupid enough to attempt to use Evasion Instinct in some suicidal attempt to force the 5th gate open.
Evasion Instinct should really be called Survival Instinct. Remember that it is capable of controlling his body involuntarily prior to his acquisition of Instinct Control. But with Instinct Control, Kyunwoo is able to ignore its commands to flee and actually force it to ensure his survival through other means. This actually happened with the goblin battle where he acquired Instinct Control. That sudden burst of strength came from him forbidding Evasion Instinct from providing Flee as an option. This forced it to instead grant him hysterical strength and Blue Thunder which is how he made short work of the goblins. However, he pushed too hard with that hysterical strength which is what led to the muscle pains for the next few days. This is how he passes this test once again. Evasion Instinct begged him to run away from the impending Mana Explosion because it could actually kill him. By refusing to run away, he forced Evasion Instinct to once again grant him hysterical strength and that gave him the extra boost needed to force the last gate open.
Cut content this chapter: Haneul and Kyunwoo's banter between her test and his test. Haneul complains about Haerang staring at her super hard during her test and feeling like he was going to devour her. Kyunwoo realized Haerang was just itching to fight a strong opponent and reassures her that he'd devour Haerang in return. Kyunwoo thought he sent across the message as "Only I am allowed to tease you". Haneul interpreted it entirely differently.
Future content:
Min Arin: The OG Mage from the game. Kyunwoo hated using her in the party and raised Haneul to be the perfect Mage that has no weaknesses. The thing about Mages is that they rely heavily on magic so their physical fitness sucks. This is especially true for Arin which becomes a running gag. Kyunwoo told Haneul to do so much physical training all those chapters ago for this very reason. He absolutely hates the idea of a Mage that fires off one big spell and then hides in the rear for the rest of the fight. Like a certain EXPLOSION mage. It is no coincidence that Eunbi forces Arin to cosplay as "a chuuni mage named Megumin" as a penalty game in the future.
Cha Eunsol: She fights using contracted elemental spirits. She is a lazy genius, eats a lot, and is mostly deadpan. Her dream is to reincarnate as a pet pig so she can just eat and sleep all day.
Nam Yuri: A walking Full Metal Alchemist reference. She literally fights by clapping her hands together and transmuting the terrain or transforming her body parts.
This is not going to turn into a harem. Only one of these girls develops a rivalry with Haneul and it's pretty obvious who. Arin and Haneul will be compared against each other for basically the entire story due to their overlapping roles.
