[1] 百万馬力 (hyakuman bariki), which means "one million horsepower"; what she's probably trying to say is 百万力 (hyakuman riki) like in story 3, which means "very strong."
[2] Rino's line is 旅は道連れ世は情け無用 (tabi wa michidzure yo wa nasake muyou), which has been misquoted by adding 無用 (muyou) at the end. Properly quoted, this is a Japanese saying meaning "just as it's important to have companions while traveling, it's important to care for one another in this life." 無用 (muyou) means "useless", which inverts the meaning of the last part, i.e. "it's useless to care for one another in this life."
Scene: Inside a cave.
Rino
Hey, big brother! Meeting you here feels like a million trucks! [1]
Rino
Hi! It's Rino! I'm doing well!
Rino
What are you doing here, big brother? Are you on another walk?
Rino
Uh-huh. You heard that the inner structure of this cave was changing, so you took on a request to investigate it? So you're here for a job, then! Good work!
Rino
(Umm... The inner structure of the cave, changing... Could that be because of the guild master?)
Rino
(Thinking about her, could changing terrain be a use of her power to change the shapes of objects?)
Rino
(Now that I think about it, she did say something about making a secret base around here...)
Rino
(If she shifted the terrain to do that, then the structure of the cave must have changed.)
Rino
... Huh? You're asking what I'm doing in this cave?
Rino
I'm doing that thing -- gathering materials for making clothes! They're the same clothes that you helped me get those special plants for, earlier, you know?
Rino
Thanks to you, even though the process was difficult, I ended up making the dyes. But I don't have the fabric that I want to apply it to yet, so I've been collecting the materials for that lately.
Rino
That fabric can be bought pretty cheaply in stores, but if I collect everything myself, then it'll save even more money, right?
Rino
Ahem, it's an investment for the future! I can practice my skills, and at the same time, I can cheaply get everything for making the clothes! A thrifty girl like Rino will make a good bride one day, huh?
Yuuki
1. That's right.
2. Is it okay that you're not studying?
Option 1.
Rino
Heh heh, it is, it is! It's okay if you take me as yours, you know!
Option 2.
Rino
Eh!? N-No, um, I'm also studying...
Rino
I'll definitely pass the test next time! I've been studying hard every day until late night, you know?
Rino
This is, um, just a quick breather from my exhausting studies! Since I'm applying to a fashion school, it's important to have practical experience too!
Rino
So, um, it's not good just to sit at my desk! No matter if it's making the clothes, or gathering these materials, it's all like I'm studying for the test!
End of branches.
Rino
Anyway, big brother, you're not super strong... It's dangerous for you to be exploring on your own. Some pretty strong monsters can come out in this cave.
Rino
I'll help protect big brother! And in exchange, I'd be really glad if you could help me gather the materials I need.
Rino
Like they say, a friend in need is a friend you don't need! Okay? Then, let's go! [2]
Rino
So... The thing I'm looking for is this spider monster.
Rino
It's supposed to appear in this cave. It spins a rainbow-colored web, which is a really good material for making clothes.
Rino
The spider absorbs pigments from the food that it eats, which seem to get into its silk and produce that rainbow color. That also means that the silk is really easy to dye.
Rino
It's the the best material for the dye we got earlier! And if you don't care about color, the threads start with that rainbow color, so you can use them in any outfit.
Rino
I want to get as much as we can. But that spider is a really strong monster, so if we can, we should try to gather it without being noticed... Big brother?
Rino
Huh? Big brother, you're gone!
Rino
Where'd you go? Don't just go away like that! It makes me feel lonely! Big brother!
Rino
Huh? There's a voice coming from right above me! That voice... BIg brother?
Rino
Why are you up there? Wah, the spider was hanging on the ceiling of this cave all along!
Rino
Big brother got trapped in its web, and now the spider's going to munch on his head! This is bad!
Rino
I, I'm going to save you! Please, hold still!
Rino
Uhh, big brother's in the way of the spider! No -- is it using big brother as a human shield? It's pretty clever!
Rino
(Wh-wh-what should I do? I can't just shoot through big brother, but if I don't do anything, he'll be eaten!)
Rino
(Huh? Big brother's nodding towards the ceiling? What does that gesture mean? I don't get it!)
Rino
(Ah... If I break up the part of the ceiling that the spider's hanging from, then it'll start swinging around everywhere?)
Rino
(Right. Because the structure of the cave has been changing, the bedrock has also gotten warped and fragile!)
Rino
(I can't take out the spider in one shot because it's too strong, but if I aim for the ceiling...)
Rino
(It should get badly damaged from the fall, and if goes well, maybe it could even end up trapped under rubble.)
Rino
(Big brother will fall, too, which could be dangerous, but I'll find some way to catch him!)
Rino
Okay, I understand, big brother! Here goes! Please hit!
Rin shoots.
Rino
Nice! I can really do these things if I try!
Rino
The ceiling is collapsing, and the spider is about to fall! It looks like it's cutting its thread and running away? Then, I just have to catch big brother...!
Yuuki falls.
Rino
Ahh! Oh... I guess, considering my strength, there's no way I'd be able to catch him. We both fell down!
Rino
Are you okay, big brother? What a relief that you're not hurt, hee hee...
Rino
Um, sorry, but could you move? I feel like you're flattening me, and I can't move at all... Oh, you're all wrapped in thread, so you can't move either, huh?
Rino
Uh, I brought a thread cutter, so I'll get all of that off of you, one loop at a time. Just wait a little bit, okay? We ended up getting all this thread without a problem, so this was a success after all!
Rino
You're thanking me for saving you? Nah, I'm the one who owes you!
Rino
Even since long ago, you've always been bringing me all sorts of wonderful things!