Throughout the series, Popp makes very human mistakes in the series, such as:
In contrast, instead of making mistakes, Dai has bad things happen to him - such as having his sword broken by Vearn. The tragic loss of Baran is also not the result of any actions by Dai, but a plot line.
In the beginning of the series, readers see Popp literally run away from his companions who got in trouble with monsters. He later reluctantly returns, but at that point readers were so fed up with him that many wrote to the publisher to ask for Popp to disappear from the series. Ouch, but understandable.
Slowly but surely, Popp grows up, with Maam being a big driving factor. At the same time, Maam’s opinion of Popp changes as he grows, and eventually Popp earns her respect.
Towards the end of the series, Popp plays a big role in the final fight with Vearn. In one memorable scene, Vearn throws his Kaiser Phoenix to Popp and Dai. Popp, standing half naked in front of Vearn, points his bare hands into the Phoenix’s mouth and tears it apart.
In the official guidebook, there is an image1 showing all the battles in the series and who participated in each:
The highlighted column is Popp. He is in all of them! Dai missed some fights when he lost his memory. He is just as important as Dai, if not more.
Popp’s relationship with Maam is an important element in his tremendous growth. If they were in high school, Maam is like the popular girl that many boys want, with Popp being one of them (and Hyunckel being the cool athletic guy that many girls go after).
If Popp had confessed to Maam in the beginning, she would have shot him down immediately. Good of him to chicken out that first time. After fighting with Sigma, he properly confesses to her. At this point, he’s changed into a completely different person, and Maam’s perspective of him changed a lot as well.
However, love doesn’t come to anyone easily, including Popp. Just because he morphed into a mature Sage and helped save the world doesn’t necessarily grant him a free pass to mutual love. As a result of Popp’s confession, Maam returns an ambiguous response, basically indicating that she can’t choose between Popp and Hyunckel at the moment. She’s clearly not ready. And we basically bring that ambiguity all the way into the end.
Next we look at Popp and Hyunckel.
1 Imgur - from this thread on PTT