Rotate humanoid character limbs by dragging them realtime

I want to be able to drag a humanoid characters
limbs and have the rest of the arm/body rotate
automatically to the best position.

I would like to do this without using the animator
as I will be making the movements in real time
similar to the game qwop.

How should i approach this?

 

Inverse kinematics. Here's a 7 part introduction that I found helpful: https://www.alanzucconi.com/2017/04/17/procedural-animations/




Be prepared for a lot of work.