Togusa can never quite accurately predict what Koutarou's mood will be on his birthday. Family is a sore subject to bring up, and Togusa doesn't want to be a social bother, a burden to make Koutarou have to hide what he's feeling.

But if Koutarou needs a distraction, and he is in the mood for company and a celebration, then leaving him alone on his birthday would be a worse idea. And, besides, he's been meaning to catch up to Koutarou and show him an odd book he found in his collection.

So, it starts off with a texted animated birthday greeting. He'll gauge Koutarou's reaction from there.