I really love Ru Da because at the end of the day Dan-i is significantly more comfortable and open with him than anyone else, and he is actually way more considerate of her feelings than the rest of her harem as he's never had to have a confrontation to notice and address how she feels. From his perspective too, they're bad friends who Dan-i is uncomfortable opening up to, and she seems to feel burdened by her friendship with them, while they're all caught up in their own BS (especially around their personal crushes for and obsessions over her). The insane jealousy everyone has over her being capable of being friends with/close to other people is hilarious but also not normal, which is probably part of why all of her current classmates, who know what chill is, are shipping her with Ru Da so much.
I have a terrible case of rooting-for-rival in like basically every series, but at the end of the day I like Ru Da better for how he forces the dynamics between characters to be reevaluated than for being a love interest. He's mean to the harem but he's also not wrong. It's long past time the boys started really trying to shoot their shot, and quite frankly, her taking a confession at face value benefits everyone after her, even the first confessor who will inevitably get shot down.