So far Kartik and neil both are looks like a recurring character. Both are shown when needed to drive the story forward, else they are not in the scenes.
They are not minor, but not even the main characters. Both can be categorised as key characters which keeps coming and going back.
Bdw, makers should start a little revealing about Neil an his backstory instead of always magically appearing him wherever yuvika goes. It's high time, his individual scenes with vidur, and other mahajan should shown to understand his properly and his equations.