Imadoki no Vampire: Bloody Bride

First of all, you must be able to date a human girl that day/eve if you wish to exploit this glitch.
Once Lilicca and Karen stop answering your phone calls, call any girl and invite her to a date with you on the day you wish to date either Karen or Lilicca.
After that, immediatly use your phone again to call either Karen or Lilicca.
Neither of them will answer the phone, but when you go on the date, you'll meet them instead of the partner you set yourself up with!

This is an excellent way to meet them at eve without having to work for their affection first!