Here is a guide on how to find all 9 weapons in Immortal Planet.
Assault Blade, Shieldaxe and Swordspear.
Choose one of these at the start of each game.
Can be found at in the temple after killing the boss. Head south in the boss room. In the next room you will find 3 cages at the sides. Open them to get all starter weapons.
Opening the temple area and Mace
Talk to the frozen archivist until he offers you the shop.
Here you can buy the mace and blood. After buying the blood you can enter the temple (head NE after the first boss fight where it says “area closed”).
Near the frozen archivist you will find a hole. Jump into it. At the NW corner you cann pick up the blade.
Head south after killing the temple area boss. You will find a merchant selling the spear.
Head towards the archives area. Near the platform you will find its owner. Talk to him and kill him after.
In Fortress area: Find and talk to the guy watching the paintings. Kill him.
Talk to the guy at the prison and kill him.
After getting the gunaxe, the razor blade and the cryo saber head to the temple. In front of your save spot is a statue that was locked before. Use it and fight the 3 enemies.