Where to find
Both steel and piece of metal can be found from ghost (the grim reaper looking monsters)they require a high drop rate to drop which is why it is hard to find.
Caligos Weapon is the strongest weapon the effect of it is CRI 10% str 50+
How to get the red necklace (superstar)
Start by going and making the hulahoop necklace (sealed necklace - any s ranked chest or root of Forrest. Silver necklace buy from nering). This gives you the option to make the "kiss me" necklace. This will allow you to make the superstar necklace.