Leo
Splinter wanted to teach and prepare you to become a better kunoichi. He helps you meditate and become stronger with your (weapon).
Raph
You asked Splinter to help you with your stealth abilities, which he gladly accepted. He even helped you prank Raph using your stealth once you mastered the ability.
Donnie
You sat with Splinter, talking over tea. Somehow, the two of you began talking about shipping and otps. Splinter continually tried to use his new fangirl vocabulary for the rest of the day.
Mikey
Mikey dared you to teach Sensei some of the new dances of today. You took the challenge and attempted to teach him how to whip, dabb, hit the folks, and even nae nae, which all lead to him failing miserably.
Casey
Master Splinter made (favorite dessert) with you. He often does this with you to surprise Casey and his sons when they return from patrol.