To reach Dr. Sayasa: west (diagrid), east (spin), northeast, southwest (movegrid), northeast, west, southwest. If you want the items and tamers, too... here's a labelled map.
Head east, and battle Motoi. Collect the 2x Balm++ from the northwest corner. Follow the room around to battle Hidetaka and Takeshi & Yuka. Following the room further takes you to Shunsuke & Atsushi, but we'll come back here later, so touch a laser and die.
Head west to the diagonal grid room ("diagrid"), then northwest across the grid. Collect the Taser from the linked small room, then touch a laser and die.
Head west (diagrid), then east to the spinning laser room ("spin"). Battle Hideo, then head south to battle Shunsuke & Atsushi in the linked room.
Head northwest, battle Masashi, and then head back southeast (to Shunsuke & Atsushi), northeast (to Hideo), and then northeast again (past the spinning laser emitter).
Head west, battling Robyn, Madoka, and Natsuki & Satsuki. Then head northwest past the lasers, battling Momoko, and into the flat grid room ("flatgrid").
Either die and return to the room you fought Robyn, Masashi, Madoka, Natsuki & Satsuki, and Momoko in, or head back southwest across the flatgrid. Then head southwest again to battle Ayana.
Take the link by Ayana to the room with the moving grid ("movegrid"). When in here, make sure to stay close to the right wall, and carefully make your way to the northeast corner.
Head west, battling Kyomi, to the next room. Follow the room around, battling Fumiko & Megumi, and then Romi, until finally reaching the link that takes you to Dr. Sasaya. You saved your Temessence phial for this, right?