When does a Chain level up?

When does a Chain level up? - White Rope on White Table

When killing the same kind of enemy you build up a chain and after a high enough chain it "levels up" where the drop icon changes and at high levels you can recover HP and gain status effects like Protect and Shell.

But when i was doing some grinding in the Estersands when i was killing Wolves i noticed that the chain did it's first level up at different numbers, once was on 22 and another was on 8.

so when does a Chain level up?






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Dazy Chain - Level Up (Official Audio)




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Images: Mathias Reding, Archifashiondesign, Giallo, Artem Beliaikin