Ok so this has been in my head for the entire day. This is a slightly long au post.
I’ve seen the idea that Tadius can’t fight (which is great btw love that for him). But what if he did know how to fight or at least he knows how to defend, but just in a very different way that regular knights are taught.
Imagine Tadius getting his job as the Prince’s right hand man and being taught how to defend the Prince if there is an assasination attempt (or because the Prince is the Prince someone he hits on trying to stab him). Tadius gets taught from the very beginning that if need be he should sacrifice himself to protect the Prince.
So imagine a Tadius who knows how to defend, who knows how to tackle people, and get in between the threat and the Prince. But also imagine Tadius knowing how to deal with being stabbed, how to stitch himself up, how to take care of bruises and black eyes because the Prince just had to hit on that woman (she had a mean left hook).
Tadius has it ingrained in his head for so long that it’s instinct now. Take the hit, move the threat away, and make sure they don’t harm the Prince. Because even though he hates the Prince, even though he thinks the Prince is vulgar, childish, and not fit to rule, he has sworn to protect him. It is his job, his duty, his purpose.
Now imagine a Tadius that has been protecting a man that he hates finding himself with a monarch that he admires, looks up to, deems worthy of their position. While I don’t think this Tadius is self-sacrificial, (he’s pretty good at deescalating and the worst he’s gotten is probably being stabbed nonlethally) he’s learned to put the life of royalty over his and when it comes to Ella all bets are off.
Some more ramblings below
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I’ve seen some fics that have Hop-a-lot challenge, or mentions challenging Tadius to a duel. Imagine Tadius agreeing, and Hop-a-lot finds that he’s not bad. His footwork isn’t great, and Hop-a-lot can tell his sword skills are rusty, but overall Tadius is good. Obviously not to Hop-a-lot’s standards, but good. However, there’s just one thing that stands out to the frog. It’s not like Tadius keeps himself open, he can parry fine, if not a little sloppy. He fights like he can’t get hurt or at least like he’s not afraid of getting hurt.
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I know that this doesn't exactly fit with Tadius letting the Prince get decapitated, but I think that it would make sense that being faced with three trolls Tadius froze. A very deep primal instinct within him went “SHIT SHIT, NOPE, GET OUT, RUNRUNRUN.” Because honestly I feel like no matter what training, facing three trolls is going to make you want to book it.
Maybe after seeing the Prince die Tadius books it out of there and starts planning. “Oh fuck, the Prince just died, I failed my one job. What am I gonna do???” Then maybe puts the pieces together of Ella being the mystery woman and how she could be queen. He kinda likes that idea so cracks knuckles “Time to commit regicide.”
I’d like to think that while Tadius is somewhat distraught over the Prince’s death (since he has sworn to protect him and now he’s dead and ohmygod I just broke my oath) he is not that upset about actually killing the king. He made up his mind and has already accepted that Ella is going to be the new queen, so he doesn’t see the king as royalty he needs to protect.
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Also thinking about Tadius going with Ella to town, maybe a bit after Ella becomes queen. Someone tries to attack Ella, maybe upset with the whole royal family dying in one day. Dagger in hand they try to lunge at her. Before Ella can defend herself or dodge out of the way Tadius grabs the person's arm, trying to redirect their momentum away from Ella but ends up getting stabbed. To Ella’s surprise/semi-horror he doesn’t seem to be affected by that and manages to take the attacker down and pin him to the ground.
As they’re waiting for someone to call the guards and take the attacker away Ella is half mentally, half physically freaking out, because “We need to get help. You just got stabbed! What do you mean ‘It’s fine’?!” Ella is not happy to hear that Tadius is used to situations like this and is not hearing his explanation of “Don’t worry”, “It’s my duty”, and “I’ve sworn to protect you.”
She is distraught to learn about all of the things he had to learn and do, about how he was willing to lay down his life for the Prince, and how he is willing to do the same for her. Ella is done with losing the people she cares about and she’s not going to lose another to some random citizen in the street. She’ll try to show Tadius that he doesn’t need to risk his life for her. She appreciates that he wants to protect her but she can also protect herself. After all she is made of starlight and magic and has defeated three trolls. Ella’s going to try and get that through his head, but in the meantime she will be there to patch him up after every bruise and stab wound.
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TLDR: Basically what if Tadius was like a secret service member and was taught to lay his life down for royalty even if he hates them. And Ella has to teach him that she wants him to live with her and not die protecting her.
The way that Lizzie just ghosts throughout his base. This man loves his wife so much he will go to the ends of the earth just to recreate her in his HC base.