Pikari whistled all the time.
Teko wouldn't be able to tell when she had started to notice, but she knew her friend always whistled when she was happy, when she felt content. Sometimes it annoyed people. Like when Pikari's grandmother was taking a nap or when they were in class and their teachers were explaining something. But most of the time, people didn't even notice when Pikari whistled.
But Teko did.
She noticed when Pikari was whistling while changing, excited to go diving, or because her grandmother had told her she was cooking her favourite dish, or just because she was happy in general.
Teko found this habit adorable. Especially because when she knew Pikari was happy, it made her happy too. She was glad she had noticed it, every time she learnt something about her friend, she could feel her heart beating faster and her chest tightening. She knew what those feelings were and she would never be brave enough to confess, but being close to Pikari was enough.
So when they were walking home and Pikari was quietly whistling to a tune she didn't recognise, Teko simply smiled softly to herself, enjoying her friend's hand brushing against hers.