In Japanese, you say "hi" as:

• こんにちは (Konnichiwa) - This is the most common way to say "hello" or "hi" during the daytime.
• やあ (Yā) - A more casual, informal way to say "hi," similar to "hey."
• おはようございます (Ohayō gozaimasu) - Used in the morning, meaning "good morning."

So, for a general greeting, こんにちは (Konnichiwa) is your best choice!