It's not bad, but I do feel like you're trying very hard to shoehorn Jecht into the Fire Emblem setting. While I'm not inherently averse to using characters from other canons when it's done well, my usual rule of thumb is "If you don't have to, don't."

Also, just my feeling, but I think the character would be better if you dropped the weapons entirely and just made him a Taguel. It's been 10+ years since Awakening at this point, it's very possible that other tribes of Taguel could have appeared that Panne and Yarne didn't know about (as both of them claimed to be 'The Last of the Taguel', though neither of them seemed to know for sure that this is the case and Panne even seems to doubt her own claim, as evidenced in one of her supports with Gaius).

Of course, I'm not the GM, so feel free to ignore me. Simply my two cents, as it were!