What kind of person is the Player Character?
This is a bit of a rant, sorry! Tldr; I think player has to be a spineless people pleaser to go along with Carmine's lie during the festival given that Carmine was such a jerk up to that point. Read on for rambling!
I am of the opinion that if there was an option to tell Kieran the truth about having seen Ogerpon during the Teal Mask, in that narrative branch Kieran wouldn't have had a meltdown that led to him becoming a tyrant during Blueberry Academy.
But the player can't tell him the truth. But why?
Now, obviously, Kieran serves as the antagonist of both DLC - either his personality would have to be written so he was a jerk from the start, or he has to go off the deep end, otherwise there is no force to fight against that offers proper narrative payoff. Thus, the player can't tell him because otherwise there would be no story.
However, with the base game in mind, can we tell if the player character is the sort of person that would keep Ogerpon a secret just because they were asked to?
When it comes to the three main stories, they only happen because someone asked the player to do them; Nemona suggests the Gym Challenge, and the player does it. Arven needs help with Titans, why not? Someone hacked your phone and tells you to deal with a biker gang made up of students? Seems totally reasonable.
What sort of person would just do these things? A people pleaser? Someone who struggles to set boundaries? Seriously, I'm curious.
Back to the DLC; you meet Kieran and Carmine and end up partnered up with Kieran, and the player seems friendly enough with Kieran, not like they're annoyed by him at any point before the festival. (Like, I know what subreddit this is, but I'm just trying to establish that the character of the player seems friendly with Kieran regardless of the feelings of the person holding the control).
But Carmine has been a jerk to the player up to the festival. Once again - if you like Carmine, that's great, but that doesn't change the fact that if someone acted like Carmine towards you, you probably wouldn't want anything to do with her.
So, the player and Carmine see Ogerpon at the festival, and then Kieran wanders up, and the player's first impulse is to tell Kieran about it. Then Carmine speaks over the player, Kieran leaves thinking the player and Carmine were talking about him behind his back, and Carmine tells the player why she lied; to spare his feelings, was her first thought. Then she tacked on the bit about it being dangerous in the mountains.
Now, earlier in the day, Kieran told the player that he had been sneaking up to Oni Mountain for years; possibly before he even had a pokemon of his own. That doesn't mean it's not dangerous, but considering the things the player might or might not have done themselves at this point, would it actually read as that dangerous?
Anyway, the player doesn't tell Kieran cause Carmine, who has been rude to them all day, told them to. Quick reminder, the player is a teenager; is it that unrealistic that they would tell Kieran the truth just to be contrary?
If the roles had been reversed, Carmine was off playing Ogre Ousting, and Kieran was with the player, and they had seen Ogerpon, what might have happened? Either Kieran chases after it, proving Carmine right, and the player would follow - or, Kieran wouldn't chase after it, and would ask the player not to tell Carmine about it for whatever reason, and the player would probably agree...
On the subject of Yukito telling the player to keep Ogerpon a secret... once again, the player is a teenager; they don't have perspective. Just because someone claims to know better, and probably does, doesn't mean that a teen would be willing to keep a secret from someone they were friendly with. The player would have to be sort of person that folds to authority with no questions asked.
Thoughts?