Hyperdimension Neptunia is Compile Heart’s biggest series, but they do make other games like Record of Agarest War. The developer opened a countdown site with a hot present to be revealed in seven days.
If the tag is a clue, it looks like it may be related to Record of Agarest War. The tag has spaces to spell "アガレスト戦記" which is the name for Record of Agarest War in Japanese. You can also see the "ト" and "記" characters are the correct place, but that just seems too obvious. What’s your guess?