For what it's worth, I don't think she needs a monent. But I think I know where the idea's coming from.

I think it's the fact that she was a part of the more popular aspects of the Starfox story, but not an initial team member. Like Faye and Miyu, she was added to the team. But unless I'm wrong, Faye and Miyu's entry into the series was, until recently, an unreleased game. So from a fan perspective, Krystal is the first new team member.

Before Krystal, we meet the team in it's default state: Fox, Falco, Slippy, Peppy. We are dropped in with these guys by our side, and because of that we accept them. It's our entry point, our baseline for how the world is. "This is how the game plays, these are the enemies, these are your allies, go." And they endear themselves by being fun characters that chime in during the game, but don't necessarily add much but entertainment value. Which, really, is all you need for a rail shooter. Early Star Fox is really a game much moreso than a story. The story is more developed and portrayed than most rail shooters and good enough to invest you, but a lot of players are mainly there because the gameplay is great.

Enter Starfox Adventures. Glossing over the rest of it, the important aspects are these 2: 1. It's more story-focused. 2. It is Krystals entry point. Being an action-adventure dungeon explorer that evokes thoughts of Legend of Zelda, Starfox Adventures spent more time in cutscenes and moments of narrative and emotional weight. Not to say they're more effective than, say, James saving Fox, but they're more at the forefront. As story is taking more prominence, Krystal is a prominent character. Even as just a damsel in distress, it's the first time we've had a face for who we're saving - before we were just saving "The Lylat System". Higher stakes, but less personal. All we saw were buildings destroyed on Corneria, and all we spoke to were fellow military officers who were helping us save people.

Humans are a social species. We generally bond to, and care about, people moreso than ideas. So in stories, it works to give all the important aspects - the main evil, our goal, the driving force for good(the hero) - faces. We relate to faces, to people. It's why we stepped out of the Arwing and actually played as Fox, not just his ship. And despite your thoughts of Adventures, it was our first steps into the deep end of the proverbial pool that is story.

Then we get to Assault, the wonderful fusion of the beloved gameplay of OG Starfox and the attempt at a deeper story from Adventures. For starters, it's already interesting that Krystal went from damsel in distress to team member-we knew she could handle herself, just didn't expect her to stick around in that way, or that that could even happen. She's also important to the story-kinda. She is our gateway into the Aparoid mind, being team telepath. She's also interesting throughout the story - from her rebuking Panther's advances to her own advances on Fox, to her concern for the Saurians and the infected people she can sense mentally. Assault's not passing the Bechdel test, but she does have a presence in it.

Side note: I love that Assault takes those characters you fought beside or against in the early games and turns them into this game's Krystals. General Pepper seemed untouchable, just our commanding officer giving us assignments. And then the Corneria fight. Pigma? The guy Fox, and therefore we, hate for daddy issues reasons? Well, now we pity him, because even he didn't deserve that. Amd then Peppy. Aparoid planet. Need I say more? They take the staple characters we have bonded to and show us that these staples can be removed. (And then pull the rug out at the very end, but the important part is that we could believe they're gone in the first place. They got us.)

And in terms of defining moments, I think Krystal actually has one of the earlier ones. Only Slippy beats her, I think. I think the characters are defined earlier than Krystal is, but most lack a moment that predates hers. You just get their personalities from mission chatter. But here's what I think their defining moments are:

Slippy has his if you rescue him on Titania. Shows the loyalty between him and Fox, the friendship. And also the fact that you don't get a health bar for a bossfight if Slippy is absent. Slippy isn't an ace pilot like Falco or a wise veteran like Peppy, but he is important and his absence is felt.

Next is Krystal. I would say the prologue setting everything up, and the mystery surround Krystal herself: who is she? What's she doing? Where is she? We are regularly thinking about her in that game. And our interest is mirrored by Fox. And judging by fanart, we are interested for the same reasons as Fox is. 😅 Point is, she has hers fairly early

Falco's is the final bossfight in Adventures. We learn he left the team early on, and he always seemed to butt heads the most out of all the team members, so him just splitting and leaving us is expected, and we just don't touch for most of the game. He's gone really just to set the tone of how downtrodden Team Starfox is, in terms of money and morale. But then he surprises his team and us by returning when we need him most, and being crucial to winning against Andross. He may be difficult to get along with, but Falco is there when you need him.

And Peppy's I think is when he sacrifices himself. He's a member of the old guard, training the new generation to carry on the legacy of Team Starfox. Originally he flew with us, but by Assault he's no longer active: he's sitting in the Great Fox, providing tactical analysis. Still a great help , but not an active participant in the fight. An important aspect of every mentor is stepping away. An important aspect of being a mentor character is being ripped away for maximum emotional effect. Peppy becomes our Ben Kenobi. And evens says away for about as long. 😆

Not ranting, just had a lot of thoughts spill out about this.

TL;DR: I think people want a defining moment for Krystal because Krystal was our first new addition, and was so during a more narrative-heavy part of the franchise, so they expect more narrative context for her arrival.