Title : Crystal Story Awakening
Original Title : 水晶物語外伝 覚醒
Language : English (FanTL)
Developer : Dot Kobo
Released date : 2019-07-28
https://www.dlsite.com/maniax/work/=/product_id/RJ171453.html

In a secluded village away from the rest of the world, heroes are trained to fight against monsters seeking Magic Crystals. After an initial monster uprising that could tip the balance of power in favor of these monsters, three such heroes depart this village. Meanwhile, trainee Tsubame, the sister of a hero, wishes to join her brother on his campaign. Follow her lewd adventures with new monsters, new love interests, and a handful of pervs, as she journeys to meet up with her brother.

This is a “what if” story involving Tsubame, the MC’s sister from the first game by this developer. It follows how Tsubame’s journey to catch up to her brother could have gone.​