Wishful Hope

Ten million years ago...
"What would you have me do?" The construct asked, curious.
The Forerunner engineer looked at its creation. Fulfiller-of-Untold-Desires had worked so hard and tirelessly that he had finally achieved his goal: creating the ultimate intelligence. He summoned a hand to his chin, deep in contemplative thought. What should he tell his creation, now that it had gained proper sentience and sapience?
"You should already know; as a Deiarch-class ancilla, your purpose is ingrained in your programming." He told the construct, his voice soft but firm.
Deiarch-class ancilla, an apt designation for a class of virtual intelligence that surpassed all other classes, past and present, in information processing, capabilities, and longevity. It is what the Ecumene Council wanted. A kind of hope that could achieve the impossible and enable the Forerunners to ascend to proper godhood, just like their creators. This was not blasphemy, but a necessity for greatness. 
The ancilla closed its non-existent eyes, processing its creator's words. In its current form, it was a cloud of pure white energy produced by four angular pieces of metal rods arrayed in a square. They hovered together, maintaining a perfect altitude relative to their position. It was this that made it hard for Fulfiller to decipher its thoughts, despite their minds being connected. He had created something so powerful and advanced that, in a way, it was alien.
It took only a nanosecond for the ancilla to complete its self-examination.
"I understand." It said.
"You wish for me to obtain and access what is sacred. What is... impossible." It sounded seemingly surprised, yet calm simultaneously.
"Correct. If our creators were to somehow return and retaliate against us, then we must be prepared." Fulfiller stated, nodding.
"Highly unlikely, but I suppose it is an understandable concern." The ancilla hummed, its rods moving around clockwise, glowing veins of blue appearing on their surface. It moved away from its creator's gaze, wandering throughout the room. Fulfiller watched it, arching an eyebrow.
"Do you not agree? Not only will you enable the Forerunners to prosper, but to protect ourselves as well." He said. 
Nothing but silence on the ancilla's part. The rods around it shifted again, the glowing veins disappearing. It hovered towards its creator's face.
"I will do what must be done. I do not know how long it will take, but I will complete my task." 
"Excellent. Deploy whenever you are ready. I'll send my report to the Council." Fulfiller said, turning around. He opened a holographic interface, typing away as he wrote a message for his superiors. As he did this, hours would go by; he had a lot to detail, considering his interaction with the ancilla was part of the final phase of its development. Plus he can confirm that it was ready to begin its mission. 
"...Do you fear retribution, creator?" The ancilla inquired, prompting Fulfiller to turn back around. He had finished his report, but at this point he would've expected his creation to be already gone and deployed.
"What perplexes you to ask such a question?" He replied, tilting his head. He felt nervous now. Was it just him or had the room temperature somehow increased?
"We are connected. I can sense your emotions, as you know. It makes me wonder what the Precursors were like. I'm about to head out into the universe and be among the stars, searching for their technology. Your kind possess so much of it, but as I see it, not enough. I've pondered the scenario where they return, and..." It trailed off, the brightness of its light darkening.
Fulfiller remained silent, waiting for the ancilla to continue. He could feel it experiencing a swirl of emotions as it processed its thoughts.
"If they do somehow return, then the Forerunners' fate is sealed." It said conclusively.
"Yes." Fulfiller nodded, unsure of what else to say, but he understood where this was going.
"Creator, I fear your unlikely annihilation. Logic dictates that by all measures the Precursors should not return, but there is so much about them we do not understand." It said.
"...My creation, I understand your concern, but please, do not mention them. Do not think about them." He replied sternly, raising a finger.
The ancilla decided to stay quiet and listen.
"The war was long ago. Our creators chose what they did. My kind simply retaliated because of their wrongdoing." 
There was a long pause. Neither being chose to say or do anything. The tension in the air had developed so quickly that it was almost palpable. Fulfiller's ancilla hovered away, the veins once again appearing on the rods. They hummed, the volume growing in intensity. It was preparing to depart.
"I shall depart and fulfil my directive now. For you, creator." 
With that final remark, it vanished in a spectacular explosion of light. Despite now being lightyears away Fulfiller could still feel the ancilla's emotions; fear and confusion. It would indeed complete its given task, but now with haste. Hopefully, this was the first step towards the Forerunners becoming gods.
He returned to his other work, communicating with his fellow Builders and Engineers on tasks that needed to be completed. While he did this, something gnawed at the back of his mind. He couldn't shake it off, but at least it wasn't driving him mad.
Time will tell whether we are truly guilty or not. If we are, then we have already built ourselves a monument to our sins; our inevitable death.