Yuri made a decision that day. This was no small decision either. Yuri was going to do something dangerous.
Without any money life was hard. He didn't have a bond with the DWMA, so he decided to work for a witch.
All he knew is that this could make him live, and if there is one thing Yuri believes in its self preservation.
The witch's base, face , and name were unknown. All he knew is that a woman told him to stand by the DWMA'S steps at 6:30. During his wait he tried to think things over , but in the end he needed money.
Why does he need the DWMA? They don't help him at all! This witch would help him. Then he thought about it. Witches often do things with out any thought of consequence. Maybe the witch was gonna experiment on him or make him someone else, but by the time he thought about this it was much too late.