Nagatsuka starts out as a lonely kid, but his whole life changes when he witnesses Ishida offer up his own bike to a would-be thief rather than let the guy steal it. He's so moved by the gesture that he decides Ishida is his best friend—and pretty much makes it his job to stay that way. He becomes protective and obsessive about the friendship, getting visibly annoyed whenever Ishida tries to hang out with other people. That said, he's genuinely supportive too; he gives solid advice and isn't afraid to back Ishida up.
Money and ambition drive a lot of Nagatsuka's worldview. He's determined to become a millionaire and treats his cash like a tool to strengthen his friendships, handing it out freely. More than that, though, he dreams of being a film director. He even talks Ishida into entering a film competition together. Neither Ueno nor Kawai can stand him, and Ishida himself gets uncomfortable with how quickly Nagatsuka takes his side without really knowing him.
When his film doesn't pan out, most people might've given up. Nagatsuka doubles down instead—film studies becomes his college major. His failure just fueled his resolve.
Content compiled by AnimeList.moe from publicly available sources.
