We suggest to do the following steps as a first measure, as the game was most likely updated and your files might have gotten corrupted:

1. Settings -> Applications -> Vixen Wars -> Force Close;
2. Settings -> Applications -> Vixen Wars -> Clear Data;
3. Uninstall Vixen Wars;
4. Restart your phone;
5. As soon as your phone starts, direct your browser to Nutaku to download the Nutaku Android Client for automatic game updates.

Although we do not recommend this, you can directly download the game from here, but you will have to update it manually and this might cause bugs if you continue using an outdated version: https://www.nutaku.net/games/app/vixen-wars/