I think the 5B>5C is the most basic blockstring because ragna has so many options after that. If you hit them with that you can do 5D into an air combo, if they block low you can use a tk gh but be sure that you have meter to burn in case they block that too. You can do 3C to make them block low, if thats blocked just jump cancel away. You can also do a hell's fang but be warned, if they ib it you are gonna get hit hard.