|This article is about a/an location in Kamen Rider Gaim.|
The Femushinmu Planet (フェムシンムの惑星 Femushinmu no Wakusei) was a planet in which the Yggdrasill Corporation called by the codename Helheim (ヘルヘイム Heruheimu) and was the place where the Corporation discovered the Helheim Forest. It was first thought as an alternate dimension, but was actually an alien planet of the Femushinmu, sentient beings who built their own civilization. As it was where Helheim Forest was discovered, it was the first place where Yggdrasill discovered the Lockseeds.
Rosyuo began converting his people into the forms that can adapt to the forest, Inves. The Femushinmu later attempted to replicate the powers of the Golden Fruit, resulting in Kougane. However, Kougane tempted the Femushinmu to obtain the "Golden Fruit" and its power causing them to turn on each other. The Femushinmu eventually massacred each other, leaving the strongest behind. Shamubishe risked his life and sealed himself and Kougane. By this point, the Femushinmu were already close to extinction.
After noticing a small rift in space, the opportunistic Redyue sent a small seed through it. The seed found its way to Earth and grew up to become a huge tree in Zawame City and was considered as a Holy Tree by its residents.
Due to one of the forests' seeds growing in Zawame City, the sentience of the forest chose Earth as its next target, and made cracks so that Inves and plants from the Femushinmu Planet will reach the humans. Once the humans from Yggdrasill Corporation learnt of this, they considered it a threat and kept strict and confidential research on it.
On one of Yggdrasill's research trips to the alien planet, they accidentally got data on Demushu, who was classified as an Over Lord Inves, a codename given by Ryoma Sengoku, due to his unique traits, including control of the forest's plants and noticeable speech pattern.
When Demushu and Redyue learned of the humans, they became curious of them. Demushu wanted to know how strong they are, while Redyue wanted to use them as her pawns.
Demushu started assaulting the humans who were researching near the Yggdrasill crack and was defeated by the combined efforts of Armored Riders Gaim and Zangetsu Shin, he was punished by their king afterwards.
When Takatora Kureshima was betrayed by his so-called allies, he was saved by Rosyuo and explained to him the history of the Femushinmu. After hearing Takatora's story, Rosyuo deduced that the Humans were the same as the Femushinmu, and therefore needed to be wiped out.
At that time Kouta Kazuraba and Kaito Kumon started pursuing Demushu, the Over Lord saw a crack and flew through it. DJ Sagara appeared before Rosyuo and Takatora and asked the king if he can give another leeway for his chosen champions to gain an advantage. During these events, Redyue offered Sid and Micchy the way to the Forbidden Fruit. Rosyuo gave Sagara a key, made from a portion of the Forbidden Fruit of the Femushinmu, and as Sagara left to give it to Kouta, Sid appeared claiming that he will acquire the Forbidden Fruit for himself, which led to his death by Rosyuo's power.
After Sid's and Demushu's defeats, Redyue started an assault on Yggdrasill Tower, drowning and capturing any humans in it under the plants. Rosyuo went to the tower after Redyue invited him, but was surprised to see the missiles flying towards them. Amused, he showed Takatora and the humans the power of the Forbidden Fruit, and destroyed the missiles safely.
Returning to his throne, Redyue confronted Rosyuo of the power given to one of the humans, only to be subdued by the king. Redyue then proposed a plan to revive their queen using the life essence from the captured humans, with which the king agrees.
When Micchy took Mai Takatsukasa to the Femushinmu Palace Ruins, Mai showed the king another aspect of the Humans that are the same as his queen's, deciding to make Mai as her kind's Woman of the Beginning, sending her back to Earth. Kouta and Kaito arrived afterwards, intent on saving Mai, only to be told that she's already back on their planet. A battle started when Rosyuo began to test which of the two warriors were worthy of the Fruit of Knowledge, which ended with Rosyuo acknowledging Kouta. The battle was disturbed when Redyue attacked Rosyuo from behind, stealing the Femushinmu Fruit of Knowledge for herself. Due to Redyue not acquiring the fruit from a Priestess/Priest of Fate, the fruit withered in her hand. She angrily stabbed Rosyuo multiple times, not accepting that the one she had was the Fruit of Knowledge. Her methods angered Kouta, who used his powers to fix the Kachidoki Lock Seed and transform into Gaim Kiwami Arms, which led to her defeat, and the extinction of the Femushinmu. Moments after the humans left the Femushinmu Planet, the spirit of the Queen appeared before DJ Sagara and asked what will happen to the humans. She proceeded to take Rosyuo's soul, promising that they will never be separated again, and praying that the humans will not share the same fate their kind has.