エイプリルフールの神に弟をもらいました！

It's April Fool's Day today!
I (the protagonist), however, have been really into this popular game that just came out.
The 1st of April was going to end soon, but then a mysterious old man appeared in front of me.
He proclaimed himself to be the god of April Fools' and announced he was going to give me a younger brother as a gift.
A yandere younger brother, a tsundere younger brother, an inexpressive younger brother.
I'm supposed to choose one of them, but...