Honestly, that's tricky. I feel like Justine's emotions towards Holtz are pretty complex, like she looks up to him like a father figure, but it also feels like she has a romantic attachment and would've loved to spend a calm life with him, raising baby Connor. I'd say she's loyal to him, almost like a daughter. So... hard to decide. But maybe that's because I haven't watched the episodes in a while.
As for Holtz, I kind of feel like he could take or leave Justine. She was a means to an end. More girlfriend than daughter I suppose, because I never got the feeling that it'd be hard for him to leave her or even to see her die. She was there and convenient.
So, boyfriend/girlfriend, but in a very unbalanced relationship.
Maybe more a teacher/student relationship, however I do think Justine would have been willing to be more of a girlfriend, but I don't think Holtz was thinking of her that way, to him she was disposable, someone who did what he asked and was easily manipulated.
Abusive father/emotionally damaged daughter. Justine was already a mental case because of what happened to her before she met Holtz. She was looking for a father figure, for sure. And Holtz had been pushed over the edge after what Angelus and Darla did to his family, so he was pretty warped.
While I think that subconsciously, Holtz rather viewed Justine as a daughter, he didn't hesitate to torment her in some ways...maybe, deep down, he blamed his real daughter for "allowing" herself to become a vampire, even though she was just a little girl and it wasn't her fault. And though he did what he had to do (killing his daughter) I think he carried around a lot of inner guilt after that. Kind of like Gunn did after killing his vamped sister.
Holtz and Justine together was just an accident waiting to happen, with a seriously twisted "family" dynamic. And after Holtz, Justine briefly ended up with another damaged psuedo-family member: Wesley "I'll take away your bucket" Wyndam-Pryce. That girl just couldn't get a break. Karma was just kicking her ass. 😅
I voted for "father/daughter." I never sensed any romantic chemistry between them. But as others said, Holtz's part was a father who was prepared to toss his 'daughter' out the door at any time. He was just using her; Justine was the needy one. This made even more sense when I read somewhere on these threads that the storyline was originally meant for Kate.
I like @Ethan Reigns's idea better, though, as Justine really seemed willing to drink the Kool-Aid, needing something to believe in even more than a father figure.
As has already been said, I think Justine had feelings for Holtz, but they were complicated. She admired and respected him, and he gave her life real meaning. I think she was incredibly lonely and lost and saw Holtz as her rescuer. I think he saw her as a means to an end, and manipulated her to get what he wanted. If it meant showing her kindness and understanding, that's what he did, but I don't think his feeling for her ran any deeper than seeing her as a weapon to wield against Angel.
Yeah, it's pretty obvious that Holtz is using Justine AND Connor to strike back at Angel. I definitely felt he didn't really care at all for Justine, and I'm fairly sure he stopped caring for Connor once he realized he could use him to hit back at Angel again.