i clarified in my original reply: emotional incest. it is a psychological phenomenon in which a parent uses a child as an emotional replacement for a partner - using them for emotional support, oversharing details of their life that would be inappropriate for a child to know about their parent, depending on them and often affecting their personal life. a real life example would be stuff like boy moms who are jealous of their sons’ partners, who overexert their influence and rely on their sons for continued emotional support. in homestuck this takes a more fantastical form, but it totally fits the bill of dirk re-emphasising his status as an ectofather (even though this is a pretty fake and nonsensical form of fatherhood even in the original text), and using rose as his emotional crutch.

it’s also important to note grooming is not inherently sexual either. all it actually means is preparing a person for something, and in this context dirk isn’t preparing rose to be in a relationship with him, but rather grooming her into a role he wants her to play in his grander plans. the fact that grooming doesn’t have to be about attraction or sexual desire is even a plot point in the original homestuck - the biggest groomer in homestuck, doc scratch, doesnt even have capacity for sex or sexual attraction. he grooms several young girls, and zero of those instances are sexual.

i think you’re taking the text in bad faith by hyperfocusing on the common colloquial connotations of the specific words. incest and incestuous abuse and grooming have all been themes in the original homestuck, often explored through the lens of heteronormativity, and HSBC is expanding on the theme by specifically deconstructing the topic in the context of a family unit. dirk grooming and abusing rose is not about either of their sexualities, but rather a commentary on the real life dynamic steeped in heteronormativity - the dynamic of fathers ”owning” their daughters, and both the incestuous and abusive parts of that dynamic.