Rise of the Kasai

Story related and cannot be missed.

This will unlock after completing Kri (level 10). If you are having trouble with this boss, turn on the Invincibility cheat and there will be no challenge to it. The strategy:

1. Take out the large number of minion enemies before taking on the boss.
2. Once they finally stop coming, attack the spider legs.
3. When all of the legs are "knocked out", the spider will fall down.
4. Use Rau to target the floating blood crystal (the game calls it a "heart" but it sure doesn't look like that to me). With the spider on the ground the protective casing will disappear and you will see a much smaller crystal. This is the crystal you can damage so do so with Rau's bow.
5. The spider will get back up and you need to repeat this 3 more times.

The trophy will unlock as soon as the cutscene begins.