My answer is simple. Almost every korean smut with a male lead is harem. It gets generic if every single one is secretly a harem. I thought (and still secretly hope) this breaks the mold. So few do, so it's nice when it does happen.
Because if it's the mc & Seyoung then this could be a great dynamic between a tall girl & short guy. It's not that everyone is acting like they are dating or the pink haired girl is stealing him. People literally just want him to be with Seyoung.Tsundere like Seyoung are a thing but a pick me character will always be more annoying.
I already knew it was a harem and I wasn't that attached to Seyoung because if I'm being honest she's very childish with how she keeps throwing tantrums and threatening violence against MC. I don't know why everyone thinks they'll be perfect together other than the fact they keep "bantering" and banging. I was kinda put off originally by how he just wants this chick to stop smoking but then 3 broke chicks just start crashing in his place, eating his food and using his things with no regard or consideration of his feelings. Pinky hasn't really argued with MC that much she just keeps flirting and teasing him cause she's bored. I'm kinda glad that they go with the "he's actually capable of being super manly, cool and kind leading to girls falling for him" and not any childhood friend crap or having him saying/doing something kind leading to girls falling for him. I like that Pinky has experience but is so caught off guard by how cool he suddenly started acting that she gets flustered and embarrassed. Everyone is acting like Seyoung and MC are dating or showing signs of reciprocating their feelings but like... They're not...? I know Seyoung might be into him but she's super childish and annoying about it while MC is just scared shitless of her outside of sex (I'm sorry but she's really not jacked and looks like she does gymnastics, figure skating or palates) and also do you think Seyoung is going to have the balls to ask him out on a date? How exactly is pinky "stealing" him when he's not even dating Seyoung they just did some sex shit. I'm glad there's a new dynamic because some find arguing good chemistry but sometimes it just feels like they hate each other. Pinky feels like she'll be a bit more assertive direct or more forward or more unlikely she'll be shy and submissive which is cute because of the gap moe. Y'all are acting like Pinky's not even taller than him and will provide the same experience. I'm all for harem route but I really can't see the brown haired girl entering the group.
(this was just a rambling of my thoughts on the matter cause too many people are dunking on her for being curious and horny about her friends fuck buddy)