You're watching a show called Nadia of the Mysterious Seas, but something is amiss. No, I don't mean the low quality of the tape. (Did you like episodes 25 and 26? LD quality!) I mean it's called Nadia, but she doesn't seem to be the main character. Although it's not my place to name a show that I didn't produce, I'd say it ought to be called Jean's Bizarre Adventure.
Even though it's completely obvious, I'll use this article to prove that Jean is the main character. In episode one, the story begins with Jean and his uncle preparing for the flying contest. Starting then and until the very last two episodes, the entire show is given to us from Jean's perspective. Jean first sees Nadia riding by on her bicycle, and we know nothing about her until Jean learns something about her. Like many other anime involving romance, the main character likes another character and the audience knows this. We don't know how that other character really feels until they say it or until their actions reveal it, but we know the main character's feelings from the start. Godai of MI for example, from the first time he sees Kyoko, we know that he thinks she's gorgeous. At first, Kyoko has no interest in Godai, and we know almost nothing about her emotions for several episodes. Even then, we are in constant contact with Godai's thoughts and dreams, his feelings and troubles, while we only get chance glimpses of Kyoko's slowly-growing attachment to him. It's the same in Nadia. We know how Jean feels and what his hopes for the future are, we see his dreams, we share his difficulties with Nadia, but we're given very little of her side.
The island episodes really show that Jean is the main character. We see Jean working to make the island livable, we see Jean try and deal with Nadia's vegetarianism, we get Jean's perspective of misunderstanding in the relationship, especially regarding the smooching. If Nadia were really the main character, we'd see her struggle with love for Jean that gets blocked by his lack of understanding for her different ways. We don't get that, but instead we get Jean's love for her being smashed repeatedly by her stubborn and cold-hearted attitude. It's Jean to whom Nemo comes in a dream and gives advice, not Nadia. Now I'm gonna give a bit of unimportant spoiler here, so watch out: In a later episode (my favorite, episode 34), Jean composes a song of love for Nadia. Since he's the main character, we get his perspective of asking others for advice and composing the song. If Nadia were the main character, then we'd see her perspective of wondering what Jean is doing sneaking around and asking others questions, and we'd share her surprise that he wrote a song for her.
In movies and TV, who's usually the main character? The good guys or the bad guys? It's the good guys, the light side, the pure, the bright and shiny. Hideaki Anno, Nadia's director, has said that Jean and Nadia are like his own light and dark sides. So then Jean must be the main character, for he is the good, the light, and the pure.
It may be the case that Jean Loc de Lartigue is supposed to be Jean-Luc (a very common French name) de Lartigue, which means that he has the same name as Jean-Luc Picard, everyone's favorite sci-fi TV series main character. This further proves that Jean is the main character; he was named after the main character in a new and extremely popular TV series (at the time). Believe me, you haven't really seen ST:TNG until you've heard the Japanese dub (remember, Riker's and Nemo's voices are the same).
As I mentioned before, there are places where Nadia takes over as the main character. For five minutes, she's the main character in the episode with the big old whale, and in the last two episodes, she's basically the main character, but both times only because she holds Blue Water. There are lots of shows where the main character steps aside for an episode and someone else has the spotlight; what matters is who is number one for the majority of the time. It's plain for all to see that Riker is number one. Ah! I mean Jean! Jean is the main character! So next time you're asked what your favorite anime you've seen at CJAS is, you'll say, "It's Jean's Bizarre Adventure, of course!"