Kojuro first became friends with Neko through being best friends with Masamune and didn't particularly have a romantic interest in her. However, as their friendship progressed and him with the mind set of thinking "all girls are scary", she was able to change his mind. Though she didn't intend to change his mind, Kojuro's overview on Neko had him compare her with the other girls very deeply, thus leading him to realizing his sudden affections for her.
Even though he knew that Neko was interested in Masamune, it motivated him to be a bit more like his friend. Eventually he gave up, knowing he couldn't do the things that Masamune could. His attempts to prove Neko of his manliness has been leading him to immediately becoming embarrassed, leaving a very confused Neko to misunderstand.
A year before Masamune joined the school (1st year), Kojuro had encountered and befriended Aki, assuming she was very nice considering they had a little bond over sweets. It was after the athletic festival was over and Kojuro was back in his uniform did Aki realize her mistake. He hadn't known of Aki's fear of boys so when she overreacted at his gender and named him "Okamaboku-chan", he began to become afraid of her.
Kojuro would sometimes question Masamune on his infatuation of Aki, recalling on the incident with Aki to himself.