One of my favourite things about the end of The S-Classes That I Raised novel (major spoilers ahead),
is the realisation that the reason why Yoojin and Hyunjae's relationship looks so much like a love story at times is because it actually, honestly is.
Like, we know that sctir is a novel about love since the beginning, that's not surprising. Yoojin's capability for loving monsters (both literal monsters and the human kind) and the power of that love is at the centre of the plot.
But by the time you get to the end, you realise - and the author confirms this themselves in their final Note - that Yoojin's relationship and love for 2 specific people was the true core of the story, and what allows him to save the world in the end:
One is, of course, Yoohyun.
And that love is absolute; you cannot say that it's inevitable, cause we know Yoojin had to make a choice when he was a child between Yoohyun and his parents, and he almost chose his parents, but from the moment he decided to love Yoohyun onward, then it was unconditional and eternal. It's the love of a brother, but also the love of a parent and a caretaker.
And the other person is Sung Hyunjae.
And that love is not unconditional nor inevitable or absolute at all. It's not something that can be taken for granted. We actually see, because of how it ended between them before the regression, and thanks to the White Bird's power of seeing possible futures, that there were so many timelines where Yoojin and Hyunjae would have never come to care about each other fully (tho they are always at least somewhat interested in each other, because their personalities are actually really compatible).
But the White Bird also sees that the only possible future where the world is saved is the one where they love and hold on to each other. And that is how the story goes!
So, just like a romance novel, the necessary end is the one where they both love each other and accept that love. And it's not easy to get there! It's a slow burn.
From meeting to getting to know each other, appreciating each other's skills and intelligence, finding out they have fun together but still not trusting each other, to working on building that trust.
They go from a strong but superficial mutual interest to actually caring about each other as people.
Yoojin has to go through the self-doubt of feeling inferior and fearing that Hyunjae will lose interest in him. Hyunjae has to learn to stop pushing Yoojin away because he doesn't know how to handle having someone he cares about so much, and also someone that cares about him, because nobody in the world (except in part Song Taewon) likes Sung Hyunjae as a person, he is only ever admired from afar.
And in the end, after going through ups and downs and a few "break-up arcs", they make it. They accept their own feelings and each other's feelings.
And that's when Yoojin makes the choice to use the power that the transcendents gave him at the very beginning of the novel, to save Hyunjae. Not the world. Not even Yoohyun! Just Sung Hyunjae!
Yeah, the whole "gather 50 S-Class people", the very thing that gives the novel its title. That is not a power that is used to save the world!! It was meant to, but Yoojin is "selfish", and he will always choose to save the people close to him first.
And being able to love someone so selfishly gives Yoojin the power to save the whole world, too. As a bonus! A reward. Just a side effect.
So yeah. Is it romantic love? No. Canonically, there's almost no romantic love in the whole novel.
But is it a love story?? Yeah. Absolutely it is.