“Koushirou likes Taichi a little too much.”
Well, yeah, of course he does. There’s bread crumbs in the anime, but it hits you over the head in the novels: Taichi Yagami is someone Koushirou Izumi sees as an exception. A boy who treats everyone indiscriminately. And that obviously means a lot to Koushirou, who had an incredibly hard time connecting with people. And you know Taichi really seems to hold Koushirou in some high regard, whether he himself realizes it or not. One of the first things Taichi does in the digital world is explicitly ask Koushirou for his opinion. And it’s only when they’re alone again that Taichi reveals he’s heard the word Digimon before they even came to this strange place and only to Koushirou and he listens when Koushirou shares his opinion and even when he doesn’t quite understand all of the words rather than look down on him, Taichi thinks Koushirou’s vocabulary is amazing. Before everything, Koushirou believed himself to be absolutely worthless and Taichi turned to him in a life or death situation and told him, “We rely on you,” and smiled. He’s also the indirect reason Koushirou even made it to the digital world, at least at the time he does. Because Taichi–specifically Taichi–invited him to that camp. And that one action brought him to Tentomon and the whole journey helped Koushirou get closer to his parents AND IN TURN even closer to Taichi, who still openly accepted him, implied he wanted to be closer to Koushirou, that it wasn’t just his usefulness that Taichi cared about–but actually Koushirou himself.
Of course Koushirou likes Taichi a little too much. He valued Koushirou long before Koushirou even saw worth in himself and then helped him to realize it.