Lencia is probably the heroine who can join you in battle the earliest. Start off by meeting her in the park. At night of Day 2, go to the park and you will meet her. Accept her offer to go with you and she will be your partner.
After that, just go to the park during the day to ask her out at night. After the first week has passed, she will start hanging out at your house at 5pm washing your clothes/underwear (CG) and also cook dinner for you everyday. Note that by the end of the third week Lencia will be out of town for 2-3 days to visit her mother so you cannot ask her out at night at that time.
You can find the 1st crystal when you first fight Kahlua on Day 15. To find the other 2 crystals, go to all 3 of the following places: cemetry, school, and church and fight the bosses there. 2 of the 3 (it's random) will give you the crystals. After that, head to the church and defeat Kahlua and save Lencia (CG). Note that if you do not defeat Kahlua before the end of Day 26 you will reach a bad ending with Lencia (CG). After you save Lencia, then go to the underground via the staircases at where the 3 bosses are to fight against the final boss. Please prepare some recovery items and Ice Crystals for this battle. If you cannot defeat the final boss by Day 28, it will be Game Over. After you defeat the final boss, sit back and enjoy the ending (CG).
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