While playing basketball one day, Sazer-X comes across a mysterious young boy named Riki, who claims to have amnesia. At the same time, the Descal Space Pirates put in motion another scheme to defeat Sazer-X and gather the Cosmo-Capsules, by reviving the ancient enemy of the Gransazers - the Bosquito.
Tropes:
- Big Bad: The Bosquito forms the crux of the threat in this film, more specifically the Ghost Ship, which actually the dormant state of the Mammoth Bosquito, the Bosquito's Hive Queen.
- Costume Evolution: Compared to the Bosquito that appeared in Gransazer, the Bosquito in this film appear much more monstrous. Supplementary materials state that they're actually a Hive Mind subspecies of the Bosquito that appears in Gransazer.
- Crisis Crossover: Brings together all three sets of Sei Shin heroes to fight a common enemy.
- Darker and Edgier: Considering Sazer-X was in its Lighter and Softer first arc at the time of its release, it definitely comes across as this. The plot is much more grim and serious, there's fewer moments of comedy and even the Three Shoguns, who in the series were a comically inept Terrible Trio, act seriously and much nastier in this film.
- Genius Loci: The Ghost Ship turns out to be a dormant Mammoth Bosquito, the strongest Bosquito form.
- The Horde: The Bosquito in this film are a swarm-like horde that rushes enemies, although unlike the Bosquito in Gransazer they're much easier to defeat.
- Mook Carryover: At the beginning of the film, the Descal attack the city using Bulgario, a Giant Mook originally used by the Daruga Imperial Army in Justirisers.
- Mysterious Waif: Riki is a male version. He's a mysterious young boy who is connected to a number of plot developments that happen later on.
- Nice Job Breaking It, Hero: Both Takuto and Mio unleash the Bosquito threat by firing Lio-Carrier's lasers and calling upon Justi Power respectively. Since Bosquito feeds on energy, it reproduced massively upon receiving the Justi Power, as well as turning into corrupted versions of the Justirisers.
- Non-Serial Movie: Averted. This film could theoretically take place at any point between the first and tenth episodes of Sazer-X, barring some minor nitpicks like the Shoguns acting eviler than usual.
- Properly Paranoid: Ad is immediately suspicious of Riki. He's proven right when it turns out Riki is spying on them for Descal.
- The Psycho Rangers: After absorbing Mio's Justi Power, the Bosquito turn into evil versions of the Justirisers and even manage to replicate their Genseishin.
- Spotlight-Stealing Crossover: Sazer-X are the main focus of the film. While the Justirisers also get some focus throughout, the Gransazers only appear in the climax and even then they only appear transformed.
- Starter Villain: The Bulgario that Descal sends out at the beginning instigates the first mecha fight of the film.
- Super Team: The Gransazers, Justirisers and Sazer-X all come together to form one big team to battle the Bosquito in the climax.
- Took a Level in Jerkass: The Three Shogun act much nastier in this film compared to the series. While Aqual is established to be a manipulative ambitious schemer, both Blaird and Cyclead are more or less Punch Clock Villains. Blaird is a Noble Demon who wants to defeat his enemies in honorable combat, while Cyclead cares more for inventing stuff than killing his enemies. In this movie, all three pirates gleefully manipulate a child into working for them.
