Tohka Yatogami is one of the main female characters of the Date A Live series and the first Spirit saved by Shido. There is also another personality named Tenka residing inside her, which only emerges when she assumes her Inverse Form.
When Tohka first appeared on Earth, on the 10th of April, she came under attack by the AST. That was also the same day Shido encountered Tohka and later discovered the real reason behind the Spacequake incidents. The next time Tohka encountered Shido, she was again under attack by the AST.