Why is it called the Vic Viper/Warp Rattler? Because the Options trail behind it in a serpent-like fashion, and the iconic front fins are designed to invoke the image of a snake's fangs.
Not to mention the covers to versions of the game branded as "Salamander" feature the titular creature represented by a flaming snake. While it could refer to the Segmented Serpent enemies featured in most of the games, they never factor in the plot.
the creature only factors into the plot for Lifeforce, ironically. Zelos is not treated as a planet-eater in Salamander's canon.
Gradius V features an in-game and plot-relevant moment of fridge brilliance, but it's neither the only time this occurs in the series nor the troper's story...
The obscure (even for this series) Nemesis II (also known as Gradius: The Interstellar Assault) for the original Game Boy begins with the series' protagonist spacecraft Vic Viper escorting a pair of friendly freighters, before they get shot down by a huge core, which chases the still quite helpless player (starting off with no powerups) into an asteroid. Said game ends with you speeding after the fleeing big bad, through a graveyard of large ships. This troper thought that something about the music here ("Pursuit") was unusually epic for the context, until he realized where he'd seen ships like this before: Your friends from the intro! They aren't the same ships, but he realized that the game was telling him "Hey remember how this game started? With you running for your life from a huge boss? Who's got the big guns now?"
In Gradius Gaiden, on successive loops in Stage 8, Heaven's Gate is the seventh boss you fight.
In Stage 7, why is your ship capable of flying through an area being sucked up by a black hole, the only signs of struggle being its shaking animation? Because, according to the manual, the player ships have a maximum speed of five times the speed of light.
The background music for stage 3 of Salamander/Lifeforce is called "Planet Latis". Considering that Planet Latis appears to be the home planet of Lord British, it would seem to suggest that stage 3 is Planet Latis itself. You know, that stage that appears to be made of fire. If this isn't the system's star, then what exactly happened to Latis??
The NES version of Lifeforce implies that Zelos is so incomprehensibly big, space and stars can be seen inside of its stomach. This makes sense, as the manual outright states that Zelos consumes galaxies whole. Therefore, it is entirely possible that one would only even know they were inside of Zelos if they were being attacked by its forces. With this in mind, What if the entire Metallion star system is still inside it!?