Start by having her blow them.

"So, what do you want me to do first?" she asked them both, looking mostly at Izuku for guidance.

"How about giving us both a blowjob?" Kaminari suggested, looking at Izuku as he already started undoing his pants.

"Sounds good to me," Izuku followed suit.

"So, how do I do that, Master?" Fumiko asked eagerly.

"First, get on your knees for us," Kaminari explained as he and Izuku freed their erections. She instantly complied.

"Like this?" she inquired, staring at their cocks in fascination.

"Yep," Izuku nodded, walking up to Fumiko, and lightly prodding her lips with the tip of his cock.

"Um... What am I supposed to do?" she inquired curiously as Kaminari stood next to Izuku.

Kaminari gulped, and ordered her, "Start by licking it."

"This?" she questioned as she extended her tongue and began to run it over Izuku's manhood. When he nodded, she grew more confident in her actions, and continued to lick.

"Yes. Now, gently grab Kaminari's, and stroke it repeatedly. Use your other hand to caress and play with the fleshy sac beneath mine," Izuku told her. At his words, she lifted her hands, complying with the orders, fondling Izuku's testicles while giving Kaminari a hand job. "Good, now, switch." Before long, she had established a rhythm of swapping between the the two dicks regularly, fondling and licking one, then stroking the other.

After a couple minutes of this, Kaminari said through his moans, "Good, now, start sucking on mine, and move your head back and forth on it." She obeyed, clearly enjoying herself as her mouth enveloped Kaminari's shaft, and she began bobbing her head on it. Then she switched again, jerking it off while sucking Izuku's at Izuku's signal.

She kept going for a while, sucking and stroking and swapping, until she noticed feeling Kaminari's dick throbbing in her mouth. Before she could question it, she tasted his salty discharge gushing into her mouth, and her eyes widened. "Swallow it," he grunted, his dick emptying into her mouth.

She obeyed, gulping down, before pulling off the spent cock, and taking Izuku's into her mouth to finish him off next. She didn't have to wait long, before the seed that tasted like nectar flooded her mouth. Without even needing to be told, she began to swallow that as well. She was a quick study, at least until she forgot prior to her next lesson. She pulled off, and panted, smiling.

"How did I do?" she asked.

"Great," Izuku nodded with a grin as he caught his own breath.

(Side note, if anyone wants to write a side branch covering what everyone else is doing in the background, be my guest, lol.)