It is just his nature to be like that, he doesn't quite know how to change this, and he feels that its better to be true to himself. During the conversation between Haruhiro and Ranta in volume 2, Haruhiro tried to point out Ranta's problem. At the same time, Ranta points out Haruhiro's weakness and Haruhiro even tried to shrug this off. It shows that everybody is not perfect. In volume 8, Ranta had a conversation with the enemy. The raws reader described their conversation as emotionally impactful. It is after this scene that might have lead to Ranta's betrayal.
I have only read properly from volume 1 to volume 4's chapter 1. From volume 4 to 9, I was only able to read the summary which were written by the raws reader. Up until volume 6 or 7 (if I’m not mistaken), the author would always never explicitly hints that this guy likes this girl or vice versa. Only after volume 6 (if I’m not mistaken), the romance element starts to get clear but it is still not explicit for some characters. At least we can start to make smart guess of who actually likes whom.
As of the latest chapter, the romance relationship may look like this....
Haru likes Mary? (Check volume 6/7)
Ranta likes Yume? (Check volume 7/8)
Shihoru likes Kuzak? (Check volume 8)
Later in further volume. He would discover new strength after a certain incident in another world. Enabling him to confidently engage an opponent head-on such as Ranta with more offence than defense
Particularly Mary I believe. It is depicted from her continual support of Haruhiro (though it may looked minor) from her early participation into the team and in almost every circumstances in comparison to other characters.
Shihoru is another one of the best exemplar of character growth. In the first volume, she is signified as a timid/shy girl. However, she grows to become a strong one after the first teammate's death. This growth of hers is not obvious only until the second death of their teammate. She is hardly affected by this situation in comparison to others because she has faced harsher reality before, which is the death of her dearest. Moreover, other LN readers have said that she has somewhat become a sub-leader in further volumes as she has become more aware of the well-being of her teammates.
The LN describes that those who are chosen as the Hero of Heroes (Main hero of Regular Brave) are people who had lead a miserable, tragic and horrible life. These elements of negativity are their driving will to live on. So that they could take revenge or inflict punishment to those who have wronged them.
Though having OP character is not my cup of tea, I like the chara's OPness for vol 4. The general theme for vol 4 is our OP protagonist saves a damsel in distress. It was an enjoyable read on how the MC pushes forward to save the heroine. Nevertheless, the enemy is better than the MC. In the end, the hero and the heroine failed their mission to prevent a greater conflict (the budding of plot for vol 5 and above). It was a truly heart-breaking moment for them (and me as a reader) as they endured a lot of adversaries but they finally gain naught.