Dynamics Lou+Acheflow and/or Lou+Tobias?
I'll do both, because it'll be fun, and I will never turn down a chance to talk about Lou!
Send an ask with two names of my original characters and I’ll give a summary of what they think of each other! (Or, if they never interact in canon, I’ll tell you what they would think of each other if they were to meet!)
These two adore each other... as much as Acheflow adores anyone, at least.
Lou thinks of Acheflow as the big sister they never had. Plus, they are so beyond happy that Acheflow accepts them fully, without even one questioning look. There's just no hesitation, and Acheflow is so ready to tear down anyone who would hurt or even just annoy Lou, and that's an experience Lou has never had before. They never thought they weren't cared for, but getting that instant, unconditional affection from someone who isn't family? Lou is just so excited, and at the same time, so so eager to prove themselves to Acheflow.
On the other hand, Acheflow sees so much of her mom in Lou. They have that same optimism, the same carefree and cheerful nature, the same stubbornness about proving themselves and making their own way. In a way, protecting Lou started out as an extension of saving her mom; if she couldn't do it before, she would do it this time, with this tiny teenage child who is exploring collapsing ruins and the dangerous world alone, someone has to at least keep an eye on them. But Lou's own individual quirks and personality quickly shine through, so the bond between the two does become more real and sibling-like, and there is a mutual respect between the two!
There's a bit more strain in this relationship; while they both respect each other, neither one would be happy to admit it. They do actually like each other, but they're both more similar than they'd like to admit, and it causes some clashing between the two.
They are both competitive, and since Lou very firmly considers Acheflow as their big sister, they are skeptical of Tobias' motivations and are not too fond of the fact that his interest becomes romantic, because no one is good enough for big sis Acheflow, no one at all, thank you very much. Lou also does not appreciate Tobias treating them like a little kid, or doubting their abilities, even if those worries are actually coming from his concern and desire to keep them safe.
Tobias doesn't like putting anyone at risk on his quest, and he is more than a little concerned about the small teenager that essentially jumps in halfway, leading them through a dark tunnel and haunted ruins. He also has issues with younger people being in danger because of his sisters, so he does project a little on Lou, and can be overprotective.
So while they both care about each other, and wouldn't want the other in danger, they end up fighting more often than not, because communicating their reasons for being that way isn't something they would do. But it was one of those relationships where they would be like, "You don't get to mess with that person. I know it looks like we hate each other, but we don't. That's my person to mess with, not yours. Shoo!"