Kirito doesn't have a harem, it's not canon. Girls like him because of his character and they only befriend him as a companion and a friend. Sinon and Alice don't have feelings of love for Kirito, he's only for them as a friend and a companion. Kirito and Asuna are a couple, Kirito is faithful and loyal to Asuna. This picture is fan-made, not canon. I know because I can distinguish friendly relationships from loving a person. I read LN SAO
I play SAO NTR just because Asuna is sexy and one of the waifu from SAO. For me SAO NTR is just a fantasy, I am a fan of the Kirito couple. I separate canon from SAO NTR fan hentai. The sources are LN, side stories written by author Kawahara and there is no harem in LN. The girls in the SAO anime do not try to take Kirito away from Asuna, they only respect their love and support Asuna and Kirito.
Kirito is not looked down on, and he is handsome to girls, that's why girls like Kirito because of his character and appearance. Asuna loves Kirito because he is nice, good, helpful, supports her and loyal. It's not because of his gaming skills and strength, but because of Kirito's personality and appearance. And what if Kirito is slim? A guy/girl who is slim can't have a girlfriend/boyfriend? Many people and even girls like a guy who is nice, helpful, supportive and who doesn't look down on them and especially isn't aggressive. Would you rather have an aggressive friend or a nice, good and friendly one? Because I'm a guy, I'd rather have a female friend or even a female friend who is nice, good, friendly and helpful, not aggressive, selfish, horrible.