This is the backstory on Optimus saying "I'm afraid Bumblebee tried that already" to Megatron. Just a quick scene. Set about four weeks before Optimus's death.

The barn was quiet, filled only with the soft creak of its old wooden beams and the faint hum of machinery. Moonlight spilled through the cracks in the walls, illuminating the slumbering forms of retired farm equipment and the hulking frame of the Autobot leader, Optimus Prime. He lay reclined on a makeshift berth made of reinforced steel and padding, his once-glorious frame now dulled and worn. His optics glowed faintly, their light flickering like a candle in the wind.

Bumblebee sat nearby, his frame smaller but no less steadfast. His servos trembled as he adjusted the external regulator attached to Optimus's chest, the readings faint but steady, too faint, as it fought to stabilize the sparkbeat within the great chassis. Despite Bumblebee's best efforts, the Prime's spark was failing.

"How does that feel?" Bumblebee asked softly, his vocalizer cracking slightly.

"It is... tolerable," Optimus rumbled, his deep voice weak but warm. He tilted his helm to meet Bumblebee's gaze, his optics softening. "You have done enough. Rest."

But Bumblebee couldn't rest. Not when his leader, his mentor, his father in all but name, was slipping away before him.

"No, you need more time. You deserve more time. It can't end like this. I can't... I won't let it."

Optimus's tired gaze held Bumblebee's for a long moment before his optics dimmed slightly. "Life's end is not defeat, Bumblebee. It is merely... transition."

Bumblebee shook his head, his hands clenching into fists. "You're Optimus Prime! You're not supposed to die like this."

Optimus exhaled softly, a sound like a sigh of ancient wind through steel. "Even the mightiest rivers must one day meet the sea."

The words broke something in Bumblebee. He turned to the equipment again, his movements desperate. "No. No, I can fix this. I can give you my spark energy, enough to stabilize you."

"Bumblebee," Optimus began, his voice a rumble of gentle protest.

But Bumblebee ignored him. He opened his chest panels, his movements quick but shaky. "Just... let me try, okay? Please." The glow of his spark immediately illuminating the dim barn.

"Bumblebee," Optimus said, his tone growing firmer despite his weakness. "You cannot stop death—"

"I have to try!" Bumblebee snapped, his voice breaking. "You mean too much. To me, to everyone. I can't just let you go without a fight."

With a sigh, Optimus acquiesced.

The connection was made, and Bumblebee's spark energy flowed into Optimus. For a moment, there was a flicker of strength in the Prime's frame, his optics brightening marginally. Bumblebee's hope soared, only to be dashed as the readings on the regulator began to drop again. Minutes ticked by. Bumblebee did not stop. He poured his essence toward the Prime's frame, its strength flaring and dissipating uselessly.

Finally, Optimus's chest plates snapped shut, cutting off the flow of energy. "Enough, Bumblebee," he said gently, his tone filled with love and sorrow. Bumblebee collapsed to his knees beside the berth, his frame trembling as silent sobs wracked his chassis. "I just wanted to save you," he whispered, "the same way you once saved me.

Optimus reached out, his hand resting on Bumblebee's helm, stroking it gently as one might comfort a child. "You already have," he murmured. "In more ways than you know."

In a moment of absolute indiscretion and un-pretension, Bumblebee did what felt right but might've been unimaginable just a few short months before. Like a sparkling seeking its Creator, he climbed onto the berth, his movements slow and hesitant, as though he were afraid of breaking the fragile moment. He settled beside Optimus, his smaller frame curling against the Prime's larger one. His servos clung to Optimus's side, his cheek pressed to the old mech's shoulder.

Tears streaked silently down Bumblebee's face, his shoulders shaking as he wept. Optimus's arm came around him, weak but steady, holding him close. The Prime began to hum softly, a low Cybertronian melody that resonated through the quiet barn, soothing and ancient. The sound filled Bumblebee's spark, his sobs gradually subsiding as the hum wrapped around him like a warm blanket. He fell asleep like that, his tears drying against Optimus's shoulder, his frame rising and falling with the rhythm of the Prime's shallow vents. The melody continued a lullaby carrying into the night as Optimus Prime held Bumblebee close, giving him everything he had left.

For more context on the back story on this scene, read My Legacy, Duty of Care, and Caring Comes in Cobalt Crayons. I realize this is very emotive but I imagine one would be watching their father die and feeling like they'd failed them. This is meant to be a gut punch.