The photo-printing scene with the Kitamura pictures in ep 4 — you really can't skip over this. At first I just thought Taiga was getting mad at Ryuuji like she always does. But on rewatch it looks completely different to me now.

Taiga's in a great mood, going through the printed Kitamura photos one by one. Ryuuji sets down some tea and is just there next to her at their usual easy distance.

Then Ryuuji goes,

"I was going to laminate your favorite picture for you"

And Taiga lights up, like "You can do that?" Ryuuji just casually goes "Yep, sure can"

Up to here it looks like a pretty happy little scene.  
For Taiga, Ryuuji's basically offering to help her keep her Kitamura photos safe, so of course she's happy. But right after that, Ryuuji says,

"A little processing and it won't matter if you trip over yourself, or drop them in water"

And that's where Taiga's face changes. And the direction here is unbelievably detailed. First it's just a cut of her hands and her mouth. They don't show her eyes.  
Her mouth, which had been smiling with her cheeks all flushed while she looked at the photos, shifts in about three stages:

A smiling mouth  
↓  
A mouth clenching its teeth like it just took a hit of pain  
↓  
Her emotions sinking, mouth slightly open

This is so, so good. I haven't seen this level of it outside of Toradora.

Ryuuji means nothing bad by it. He's just being his usual self. He's saying it out of plain good intentions, like "Taiga trips and might drop them in water, so I should make them durable for her." But for Taiga, it probably landed with a totally different meaning.

"Maybe Ryuuji still only sees me as someone he has to look after."

"What if I'm the only one whose feelings have been moving forward?"

I think that's the moment she notices it. I think that's the part that actually hits Taiga harder than Ryuuji realizes. Taiga was happy about the lamination offer itself. She was happy that Ryuuji was doing something for her.

But then the "if you trip over yourself, or drop them in water" line turns that happiness into pain all at once. For Ryuuji it might just be an extension of the same good-natured "can't leave this troublesome girl alone," "gotta take care of her" thing that's been going since episodes 1 and 2. But inside Taiga, it's already starting to turn into something special, little by little. So I think she got scared, but also just really confused.

"What if I'm the only one who thinks this relationship is special?"

This is the kind of pain that only happens at the very start of falling for someone.

She hasn't admitted she likes him. She doesn't even realize she likes Ryuuji yet. But her body has already noticed, ahead of her, that the meaning of the relationship is starting to change inside her. So Taiga goes quiet. Her expression falls apart. But Ryuuji has no idea. As the camera slowly tilts up onto her face, her brows are knit and she's got this almost sad look.

Ryuuji asks, "Taiga, something wrong?"

Taiga snaps back, "N-no!"

But it's very much not nothing anymore. After that, she keeps flipping through the photos in silence with this angry look. And Ryuuji, almost like he's piling on, goes,

"You don't have to limit yourself to one, you know."

From Ryuuji's side, he's just being nice. But for Taiga, that's not the point anymore. So Taiga gets mad.

"Shut up! Just wait! I'm trying to decide!"

Ryuuji's like "Wh-What's your problem?" Of course he doesn't get it. He really has no clue. And then Taiga stands up and goes,

"I'm leaving. I can't make decision in peace here, so I'm going home."  
And she just trots off home.

Here, I don't think Taiga lost the ability to choose the photos — I think she lost the ability to face her own feelings while she's right next to Ryuuji. Choosing Kitamura's photos isn't just choosing photos anymore. It's turned into something like an outlet for her feelings about Ryuuji. So running away was the only thing she could do.

What Taiga feels in this scene is probably something like the pain of an emotional time lag. The feeling that she's the only one who's moved ahead. That Ryuuji's feelings might still be back at episode 1 or 2. The fear of, what if I'm the only one selfishly feeling like this relationship is special. That anxiety and loneliness hit her all at once.

So I think all these feelings were happening in Taiga at the same time:  
Happy that Ryuuji cares about her. But maybe that's just kindness he'd show anyone. Scared that she might be the only one who thinks this is special. Annoyed at herself for even thinking that way. So she gets angry. And she goes home.  
It's such a handful, but it's incredibly human.

After Taiga leaving, Ryuuji's left there with no idea what just happened. He spaces out and kind of flops down onto the floor. Then the scene goes dark. The lights drop.

And here comes Ryuuji's monologue.

"I'd sure like to have pictures... of Kushieda."

This is just brutal.  
Taiga, who minutes ago was confused and hurt over her feelings for him and basically fled home — meanwhile the heroine in Ryuuji's head is still Kushieda. Meaning Ryuuji has absolutely no idea that Taiga might be starting to fall for him. This line is a blade he's swinging without even knowing it. And it's even crueler because he mutters it alone, where it reaches no one. Taiga can't hear it, but we can.

But there's another way to read it too.  
Ryuuji himself did notice that Taiga's reaction was off. He just doesn't know why. So it also kind of looks like he's saying his feelings for Kushieda — the "easy to understand" crush inside him — out loud one more time to reassure himself.

Like he's telling himself, "The one I like is Kushieda, right?"

But the very fact that he says it at that exact timing feels like something's already starting to slip. And it's great that they have him say it in that blacked-out, emotionally drained space. In that flat darkness, all that's left is Ryuuji's obliviousness.

And then the next day. Taiga dumps the whole job of choosing Kitamura's photos onto Ryuuji. This part's pretty important too.

Choosing the photos isn't just an action anymore. For Taiga, it's become an outlet tied to the previous day's pain. So she can't choose herself. By running from the act of choosing, her real feeling comes out — that she can't face her own emotions, or Ryuuji, just yet.

Also, rewinding a bit, there's the part with Minori's bucket-pudding photos.  
Minori comes running over going "Look, look!" and just naturally hands Ryuuji photos of the bucket pudding she made the other day.

Three of them, even:

1st: the pudding sitting in the bucket  
2nd: the pudding spilled  
3rd: a selfie of Kushieda eating it

Like — she sneakily slipped her own photo in there to angle at Ryuuji, lol.  
Ryuuji blushes when he sees it.

And since she shows different photos to her friends afterward, going by the order, there's a good chance she showed Ryuuji first. Running over to show your photos to someone first — that's basically a crush already, isn't it?! is what I end up thinking lol.

On the surface, ep 4 looks like Taiga's one-sided-crush-on-Kitamura episode. But on rewatch, it actually looks like the episode where Taiga's feelings for Ryuuji take a step forward, and she gets thrown by that step herself. Ryuuji's still looking at Kushieda. Taiga's starting to get hurt, little by little, by that mismatch. And Minori, in her own way, kind of looks like she's making small moves toward Ryuuji too.

And that's the scary part. This whole bucket-pudding photo bit looks like supporting evidence for this theory I've been quietly sitting on — my "what if Minori and Ryuuji were already into each other before the story even started" theory, lol.  
This is probably a hot take, so don't come at me too hard lol. I'm not gonna flat-out assert it here, but there are bits in later episodes you can read into too, so I want to come back to it then.

But still — Minori comes running over with "Look, look!" and seems to show Ryuuji the photos first. And on top of that, she's slipped in a photo with herself in it. When you see that, you do kind of wonder, "Is this really just sharing with a friend?" lol.

If Minori was aware of Ryuuji from the start too, then ep 4 stops being just a "Ryuuji likes Kushieda" / "Taiga likes Kitamura" one-sided-crush episode. It'd mean that, just through some casual photo stuff, the misalignment between Ryuuji's, Taiga's, and Minori's feelings is already showing.

Toradora is seriously too good at planting little bombs in scenes that look like nothing.

Rewatching ep 4 and the photo lamination scene completely changed for me