How to say 9 in Japanese?

Nine has two forms, きゅう and く. きゅう is preferred in most contexts since く can suggest suffering. You will see 九時 as くじ for 9 o’clock, which is a fixed reading, and 九人 as きゅうにん for nine people. Use きゅう for clarity in most numbers and switch to く only where the fixed reading requires it. Train both sounds with the audio so you do not hesitate when speaking.