The first Tripura king who adopted the title of 'Manikya' was-

The question asks about the first king of Tripura to use the title "Manikya."

Option A: Rajafa - There is no historical record that suggest Rajafa adopted manikya Title.
Option B: Chengthumfa - Similar to Rajafa, history doesn't credit Chengthumfa with this title.
Option C: Ratnarnanikya - This is the correct answer. He was indeed the first Tripura king to adopt the title "Manikya," marking a significant change in the royal lineage.
Option D: None of these - Since we know Ratnarnanikya is correct, this option is incorrect.

Therefore, the correct answer is C: Ratnarnanikya.