
As if it's not incredibly disrespectful to imply not only that their relationship has an expiration date, but that Isshiki WILL one day be done with Kei. She absolutely is intruding. Declaring herself to be openly available and willing to replace one of two active participants in a romantic relationship... how is this not an intrusion?

"Why does she need to be nice to them and be careful of their feelings?" She doesn't, but maybe then don't also claim that she's "strong without intruding on his (Isshiki's) space or being too forceful," because she absolutely is intruding, and she absolutely is too forceful. Just because she's not physically intruding doesn't mean it's not an active intrusion into the established relationship.
And to your second point, she doesn't suggest anything about Kei breaking up with Isshiki due to his complex; she literally tells Isshiki to come date her "when YOU'RE done with Kei," as if Isshiki's relationship with Kei is the equivalent of him using Kei like a napkin or something, to be discarded once Kei has served his purpose. It's gross, it's disrespectful, and it's offensive, especially coming from a woman speaking to someone in a same-sex relationship.
I’m not gonna lie I can’t even be mad idgaf LMAOO I like her fuck it. Like “consider me when you’re done with kei like” shiii holon lemme put u in my roster just in case. I like the way u think mama