
The problem of "I'm the hero who personally fought Gaius!" (and other derivated anthics) is that at some point you will run into too many people claiming to have done so. There's only so much space (8, if game mechanics inform our story) for people to have participated in it. Now, you might say that the ammount of people isn't a problem in itself. And you are right. The problem isn't the ammount of people; it's the ammount of points of view.
So imagine that the elezen Mister Croissant has fought Gaius in-character. You ask him about it. He says Gaius put quite a fight, killing one or two of his comrades. Then you run into the hyur Sir Donut, who says he fought Gaius in-character, too. You ask again! According to him Gaius was a piece of cake that went down easily when everyone in the attack party assaulted him. And then Lord Sandwich enters the scene, claiming that Gaius had incapacitated everyone but him, who bravely put at end to the garlean general by poking him in the eye and throwing a one liner.
And then you meet another half a dozen of heroes who defeated Gaius in-character. Yet none of them have the same tale about how Gaius went down.
What happens next is that you run into a micro-canon contradiction. Not all of those tales can be true, for Gaius couldn't kill only Mister Croissant's comrade and everyone but Lord Sandwich at the same time. Croissant's and Sandwich's micro-canons are at odds with each other. The other players, upon seeing this, will have to choose which one is the liar. Which means, most likely, avoiding the other character (or both) like the plague.
That's what you are doing by being a main piece of an in-game and official storyline: you are forcing people to either accept your micro-canonical truth ("He is one of the heroes") or have to handwave and avoid your roleplay ("He's crazy!"). It's just counterproductive.
A much better solution is what others have said already: be part of the story in a generic or tangential way. You can be part of the attack to the Castri, but not part of the group that downed Gaius personally. You can be a Scion, but not the one that rescued Minifilia and the others.
By all means pick elements from the storyline to use in your character, but adapt them so that it is compatible with as many micro-canons as possible. Being part of the main storyline in-character is just asking your fellow players to get into trouble.
Unless, of course, your roleplay is limited to a specific circle or group. Then I guess you can all agree on how your micro-canon work and be quite happy with it. That's another solution!
So imagine that the elezen Mister Croissant has fought Gaius in-character. You ask him about it. He says Gaius put quite a fight, killing one or two of his comrades. Then you run into the hyur Sir Donut, who says he fought Gaius in-character, too. You ask again! According to him Gaius was a piece of cake that went down easily when everyone in the attack party assaulted him. And then Lord Sandwich enters the scene, claiming that Gaius had incapacitated everyone but him, who bravely put at end to the garlean general by poking him in the eye and throwing a one liner.
And then you meet another half a dozen of heroes who defeated Gaius in-character. Yet none of them have the same tale about how Gaius went down.
What happens next is that you run into a micro-canon contradiction. Not all of those tales can be true, for Gaius couldn't kill only Mister Croissant's comrade and everyone but Lord Sandwich at the same time. Croissant's and Sandwich's micro-canons are at odds with each other. The other players, upon seeing this, will have to choose which one is the liar. Which means, most likely, avoiding the other character (or both) like the plague.
That's what you are doing by being a main piece of an in-game and official storyline: you are forcing people to either accept your micro-canonical truth ("He is one of the heroes") or have to handwave and avoid your roleplay ("He's crazy!"). It's just counterproductive.
A much better solution is what others have said already: be part of the story in a generic or tangential way. You can be part of the attack to the Castri, but not part of the group that downed Gaius personally. You can be a Scion, but not the one that rescued Minifilia and the others.
By all means pick elements from the storyline to use in your character, but adapt them so that it is compatible with as many micro-canons as possible. Being part of the main storyline in-character is just asking your fellow players to get into trouble.
Unless, of course, your roleplay is limited to a specific circle or group. Then I guess you can all agree on how your micro-canon work and be quite happy with it. That's another solution!