Acting On Instinct is the final Hogwarts Legacy relationship quest as part of Natty Onaiβs questline, in which youβll have a conversation with her after the fight against Harlow. During the battle against Theophilus Harlow, she jumped before you to protect you from Crucio, one of the Unforgivable Curses. As a result, she ended up in the hospital with a severe injury.
Finishing the Acting On Instinct Relationship Quest will reward you with The Avenging Gazelle Trophy/Achievement. Acting On Instinct Relationship Quest becomes available immediately after the fight against Theophilus Harlow during Harlowβs Last Stand as part of Nattyβs questline.
This means youβll have to progress the main story until youβve completed The Final Repository Main Quest.
After the fight against Harlow, youβll find Natty sitting in a wheelchair beside her mother in the Hospital Wing of Hogwarts Castle.

Speak with her to begin the Acting On Instinct in Hogwarts Legacy.
How To Complete Acting On Instinct in Hogwarts Legacy
As you approach Natty, you will see Professor Onai, Nattyβs mother, concerned about her health and asks if she is up for a visitor. Natsai reassures her mother that she is fine and wants to see you. Professor Onai warns Natty not to overdo it.
When you speak with Natty, she will be happy to see you, and youβll start discussing her recent injury. When you apologize for your role in it, Natsai will tell you not to feel guilty because she chose to protect you.

She then realizes that her fatherβs sacrifice was also based on instinct and reassures you are not to blame for her injuries. Then, youβll discuss the battle at Hogwarts and the defeat of your enemies, including the death of Rookwood and the capture of Harlow.
Natsai expresses gratitude for your friendship and its important role in her life. You both acknowledge the importance of your teamwork and the safety it has brought. Finally, you both express appreciation for each otherβs company and the visit, which will complete the Acting On Instinct Relationship Quest in Hogwarts Legacy.