His grandchild's rival [♂]

You spent your entire life growing up with Professor Oak's family as your neighbors. Daisy, his oldest grandchild, was your first crush growing up, while Blue was your rival in just about everything. Blue always had a snobbish outlook, always assuming that they were better than you. But just because your rivalry was not a violent one didn't mean you constantly enjoyed being shown up or belittled by your peer.

Speaking of whom...

“In addition to Red, a young lad I've had the pleasure to know since the day he was born, I'm also accepting my youngest grandchild Blue as another apprentice.”

Really, you shouldn't be surprised. Despite your dislike of their showboating, Blue is still one of the top students in the Academy. Just because Oak was your grandpa doesn't mean you can just coast on by with the family reputation. The youngest Oak earned their reputation as the top student during your time in school, not that you'd enjoy admitting it out loud.

While Professor Oak made no indication that he intended to call up his chosen apprentices up before the rest of the students, Blue couldn't help but grab the chance to brag and show off even more than usual.