There are several airlines you can find that offer direct air ticket booking to Ranchi i.e., Indigo, Go First, Air Asia, Air India, Vistara depending on where you board the flight.
You can easily board a direct flight to Ranchi from Delhi, Kolkata, Mumbai, Lucknow, etc. Just visit IRCTC Air portal or use App to search for the direct flights to Ranchi. You will get ample options to choose from.