Duck past Marcus to grab a Hyper Potion sitting on the floor, then keep going East and you can find a Blue Shard hidden in the dead end.

Return to Kiyo and Marcus and look to the South and you’ll find another passage- but ignore it for the moment.  Instead head off to the East and you’ll meet up with a Pokemon Ranger.

Battle: PKMN Ranger Eliza (2280 Poke, Persim Berry)
Opponent: Banette Lv 38, Golduck Lv 38

Keep going East and Bianca will exclaim about the area, telling you to look around a bit.  There are some obvious stairs to the North, but you should bypass those for now- instead pester the thoroughly unnecessary doctor.

Battle: Doctor Darek (1780 Poke)
Opponent: Swoobat Lv 38

Once defeated, Darek will offer you the service you just don’t need with Bianca along- full healing and rest for your pokemon team.

Pass the doctor going East and then head North first chance you get and you can pick up TM69 Rock Polish.  Rock Polish is a variably useful move, boosting Speed two grades (thus increasing it by its original value).  On many of the pokemon that naturally gain it, Rock Polish is borderline useless- they don’t have the overall stats to take advantage of it, or their Speed is so low to begin with that doubling it isn’t enough to let them go first most of the time.  Still, the ability to go first can be well worth a turn to many pokemon with middling speed and a very strong attack stat, and Rock Polish is available to a different array of pokemon than its Normal-type partner, Agility.  This makes Rock Polish a valuable tool- you won’t always want it when you can have it, but being able to have it when you want it makes a world of difference.