Hello, Cade, it's Noriko. Thank you for counting me in. As Young told you, Japanese originally doesn't have ‘ティ’　sound. That's why you find ‘ティ’　sound only in Katakana, which is used to write imported words from foreign countries. And F7 key allows you to change ひらがな to カタカナ; it's an additional information just in case this were new informatin to you.