[NES era] 2D action exploration game with some light RPG elements? (Longshot)

I've had the memory of this game for a long time, but I'm not 100% that it's entirely real. There isn't much to go on here, I know. :( But I'd be over the moon if I could prove this memory/game are real. I'm fairly certain that if the game is real, it's kind of niche. I've played most major NES games. I'm a very active gamer.

What I know it wasn't, but is kind of similar to in a way: Megaman, Castlevania, Metroid.

Platform(s): NES (I think, but it could've been a competitor console)

Genre: Action with exploration/light RPG elements

Estimated year of release: 1988-1993? (not 100% sure, but I'm quite confident it was 8 bit era)

Graphics/art style: I don't recall it being anything distinct.

Notable characters: ?

Notable gameplay mechanics: I think you could unlock the ability to swim. I think there were purchaseable weapons. I remember projectile, gun-style weapons but they were done in a weird way, not realistic-Contraish.

Other details: I remember there being an adventure element where you could traverse a large map screen by screen. I want to say the setting wasn't too typical. I remember typical outdoor areas, things to swim in, some platforming, etc.