While fighting Dario in chrono cross I realized that Frog also wielded the Masamune. This could definetely be a wrong assumption but do you think That Glenn (Frog) is an ancestor to Garai, the father of Dario and Glenn?
Think About it:
600 A.D, Frog is turned to his original form after defeating Lavos with Crono
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Late 900's A.D., After about 3 generations, Garai is born, Glenn (frog) is his Great Great Grandfather.
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Late 1020's A.D, Glenn And Dario are born, thus being the latest generation in the bloodline.
But that's just my opinion.