Dragon Ball Z: Fusion Reborn

Janemba formed when a teenage oni (demon) operating a soul cleansing machine in the afterlife became distracted by his Walkman. His negligence caused the machine to overload and explode. The released evil spirit essence engulfed him, transforming him into Janemba, a massive childlike demon with reality-warping powers.

Earlier scenes show the oni ignoring his duties while listening to music, establishing his careless attitude.

The crystal barrier sealing the check-in station was specifically designed to be impervious to energy attacks. This was a deliberate security measure in the afterlife, likely to prevent powerful beings from forcing their way through. King Yemma confirmed that direct assault was useless, forcing Goku to devise a different strategy.

Goku lured Janemba toward Hell because the underworld has physical limits that don't exist in other parts of the afterlife. By pulling the demon into Hell, Goku aimed to weaken Janemba's grip on reality and reduce his advantage in a realm where his bizarre powers would be more restricted.

Vegeta refused the Fusion Dance because of his intense pride and reluctance to literally merge with his rival Goku. Despite the life-threatening situation, Vegeta clung to his independence and viewed fusion as beneath a Saiyan prince. Only after witnessing the danger and under significant pressure did he eventually agree.

The first fusion failed because Vegeta forgot to extend his forefinger at the crucial moment during the Fusion Dance. This simple mistake resulted in the creation of Veku, a weak and obese fusion form that was completely outmatched by Super Janemba. The error gave Janemba a significant advantage.

The tension and hesitation between Goku and Vegeta during the fusion discussion hinted at potential complications.

Shenron explained that only King Yemma has the authority and power to restore the afterlife's boundaries. As the ruler of the check-in station and guardian of the afterlife's order, only King Yemma could reseal the barrier that Janemba had compromised. This limitation forced the heroes to focus on defeating Janemba directly rather than seeking a magical fix.

Janemba's emergence caused mass resurrection of the deceased throughout the afterlife, throwing the balance between realms into turmoil. This cosmic disturbance somehow enabled Frieza and other past villains to return to the living world, leading their zombie army to attack Earth. The invasion was a direct consequence of Janemba's disruption of the afterlife's order.

Janemba's emergence was described as triggering the resurrection of the deceased, which created chaos across both realms.

Pikkon attempted to free King Yemma from the crystal by sheer force and determination. When his direct approach failed, he insulted the barrier in frustration. This emotional outburst unexpectedly caused the crystalline substance to crack slightly, revealing a potential weakness. However, the crack alone wasn't enough to fully release Yemma.

When Super Gogeta landed his decisive assault, Janemba's massive demon form was overpowered and couldn't sustain itself. The overwhelming power caused Janemba to revert to his original oni (small demon) form, essentially undoing the transformation that occurred when the evil spirit essence engulfed the teenage oni.

Both Goku and Vegeta individually proved unable to defeat Super Janemba. Even Goku's Super Saiyan 3 transformation wasn't enough, and the two Saiyans fighting together still couldn't gain the upper hand. Only by combining their powers through the Fusion Dance could they achieve the Super Gogeta form strong enough to overpower Janemba's reality-warping abilities.

After Janemba's defeat, Vegeta reverted to a spirit form and quietly disappeared from the afterlife. This occurred because Vegeta had only temporarily regained his physical body to assist in the fight. Once the battle ended and his purpose was fulfilled, he returned to his deceased state, leaving his friends behind as the souls began returning to the afterlife.

Super Janemba is Janemba's more dangerous transformation that appeared after Goku powered up to Super Saiyan 3. Unlike his original massive childlike form, Super Janemba is smaller but far more deadly, with enhanced speed and combat abilities. This transformation represented Janemba's response to the escalating threat posed by Goku.