Gaichuu are giant insects covered in jewel like armor. They live in the dark lands outside of the artificial sunlight (especially in Yodaka and Yuusari) and attack anyone who travels along the darkened paths (they are attracted to heart). To destroy them, one must penetrate their armor with heart. Gaichuu are said to have no heart, but may be able to gain one if they manage to consume enough quantities of heart, which was proven with the Cabernet. Every Gaichuu has a weak spot or gaps somewhere along their armor. The Gaichuu cannot be killed even if you behead them, as shown when Niche beheads Gaichuu Four Roses, but can most certainly be killed by shooting a shindan into to their gap or weak spot, which ruptures their armor. These gaps are numerous, but the trouble behind that is they are hard to spot. It was later revealed by Niche's Sister that Gaichuu are another form of the Spirit Insects that once occupied the Amberground, once the Spirit Insects shed the last of their "Hearts" they became the massive Gaichuu. While the other ones who went under a special transformation became the "Spirit Amber".
List of Gaichuu:
Each Gaichuu that has appeared thus far have been named after an alcoholic beverage.
- Gaichuu Absinthe [Episode 20]
It takes the form of an Atlas beetle. It may have been involved in the death of Elena Blanc 10 years ago. It was shown to have inflicted serious injury to Zazie in episode 20. Its territories are Walrus Cliff and Hult Desert.
- Gaichuu Four Roses [Episode 4 and Season 2 Episode 5]
It takes on the form of a mantis. Its territory lies in Broccoli Forest.
- Gaichuu Cider [Episode 23 and 24]
An underground gaichuu that takes the form of a mole cricket. Its weak point is its rear.
- Gaichuu Jinro [Season 2 Episode 18]
A Gaichuu that Gauche battled previously. Its weak point is its mouth. It also has protective cover on both sides of its face that slides to protect itself.
- Gaichuu Lao-Lao [Season 2 Episode 12]
- Gaichuu Daikiri [Episode 1]
- Gaichuu Glen Keith[Episode 7]
- Gaichuu Bucker [Episode 2]
- Gaichuu Cointreau [Episode 12]
Its type appears to be huge and similar to Gaichuu Glen Keith, the centipede form. Its body is white.
- Gaichuu Corona [Season 2, Episode 4]
Its type takes on the form of a pill-bug. it appears at the top of a lighthouse at Liquid Sand River, feeding off the 'heart' of the diaries that belonged to the caretaker of the lighthouse.
- Gaichuu Cabernet [Season 2, Episode 11, 12, 18, 19, 22-25]
The most powerful Gaichuu seen in the series so far, the Cabernet initially took the form of a large dragonfly. It was seemingly killed after a powerful attack from Connor Kluff, only for it to reassemble itself and 'assume a very strange and terrifying appearance.
- Gaichuu Tequila Sunrise [Season 2 Episode 13]
1. Gaichuu names were originated from alcoholic drinks (according to wikipedia).
2. Gaichuu normally have one weakspot/gap. But the Gaichuu 'Absinthe in Season 1: Episode 20 had 2 gaps. And the Gaichuu 'Cabernet during the final battle in the anime didn't have any gaps (until Niche and her sister made a crack for the shindan to enter into the Cabernet's body).