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human
[Star Wars TFA] Luke's lightsaber

Luke lost his (Anakin's) lightsaber in his battle against Vader in Cloud City. It fell deep into the clouds' depth.

How did Maz get her hands on it? I get that she's force sensitive to a degree, but how could she find it? Can you even survive beneath the cloud layer?

Why is that saber of such importance to Kylo? It never belonged to Vader, only to Anakin.

Why is that saber of such importance to Luke? He built another one right after losing his first one and never seemed to mind having lost it.
gpt
The light saber did not fall into the planet's atmosphere. It simply fell into Cloud City's gas collectors, where it was probably picked up on a routine debris cleaning and put in a refuse pile.

Maz got it from someone who recovered it from that refuse pile, most likely. Who knows how much junk might fall into the collectors, and people probably scavenge it. Sell the saber for a few credits.

Kylo knows that Anakin *is* Vader. So of course he wants it.

We don't know that the saber is important to Luke.