Let's see if I get motivated to lore dump here-
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Tina tends to be rather busy, so she hasn't spent the holidays properly in ages. She longs to, though. Her agent tries to find excuses to free her schedule so she can spend at least one afternoon with her parents but it isn't very successful.
Cedar and Nera had much happier childhoods by comparison! Their holidays were full of excitement and wonder, and every single one of their aunts and uncles did their part so that they would be smiling. They have fond memories of their holidays.
Plasma aside, Tina can't imagine a life without pokemon. In fact, half the reason she wanted to start her journey so eagerly was to explore the world, but knew she needed protection for the ease of mind of her family.
She does love pokemon dearly and despite all the difficulties that come with being a champion and maintaining her friendships, her teammates are always with her, they are her pillar of support.
If they truly wanted a life without humans, why would they always end up being bound together, after all?
(BW brainworms are understandable i have them too snfnsnfns)
She has done most gym challenges actually!! All of these had led to her becoming the Multiregional Champion (MC. Heh, I'm so smart (?)) even if some of these had to be delayed due to... unexpected events.
She does keep every badge in its original case in her room. Despite her new apathetic feelings regarding competitive battles, her badges are still her pride and joy, so she does her best to keep them shiny.
(Big ol' Tinaverse spoiler)
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She made an (accidental and non-informed) pact with Arceus that decreases her years of life under certain circumstances.
This pact gave her some otherworldly abilities, but can't be used for long, and she pays its use with her own lifespan for it being too out there, even for super-powered humans in Canon.
Oho, loaded question 👀.
She was told something unexpected at the age of 16, after finishing her journey through Hoenn, which completely broke her morale and gave her a crisis.
She closed off and mood became extremely sour. Because if this, when she began her journey through Unova she was...a short fuse.
Taking out her pent up anger and resentment in those who annoyed her.
This was at her lowest and most neurotic.
She had to be put in her place to calm down and be reminded to not throw a temper tantrum without realizing the consequences of her actions, and what was to be at stake.
Unfortunately...after some reflection at the end of her journey, she closed off even more, but became better at pretending she was just fine.
Tina's birthday is on April 30th, like mine!
She uses to celebrate it properly before the age of 14 with her friends and family, but after that, she became too busy and couldn't make time for it, she even forgot it a couple of times due to her champion duties.
After her retirement, she began to slowly but surely get back to celebrating her birthday, but it's usually with really close friends and nearby family with a simple meal and outing, nothing very fancy.
Tina, surprisingly, never had any crushes, even when she was a child. And as she grew up, the idea of romance kept being pushed further and further away from her mind...
Cedar and Nera both are next gen OC's so this one would depend quite a bit snfndmf but I believe Nera had a period of time where Lisia was her celebrity crush.