(age 7 - 8 years later)
It had been a long time since Natasha had retired from being an agent, or as retired as she would ever be. Technically, she was just assigned to the protection of Loki, but that would be done either way. All of them had taken awhile to get over Bruce's death, but now he could be talked about without tears. Though it had taken even longer for Loki to allow either her or Steve out of his sight for any long period of time. Even now he got nervous when Steve left to do something like give a speech or assist in super-heroing those rare times he was needed.
It was understandable, given how many loses he had suffered, so quickly too. Every now and again, he might regress and need a night of cuddling or keeping everyone within his sights, but for the most part he was alright.
A very long time had passed since anyone had tried to break in, and even longer since they had managed to do so without setting of the outside alarms. So when Jarvis sent everything into emergency mode after having detected an unknown heat signature nearby them, Natasha was rusty on her reaction time.
There had been no place for both of them to hide, and with both Steve and Thor out, she didn't have much of a choice but to grab Loki and place him in the only spot she knew Jarvis could seal, the air vents.
What she didn't know was that Jarvis's sensors had been compromised, and while he had closed the vent, it was left unsealed and the little god could see everything.
He could see her fight off almost ten attackers before finally being taken down by a needle to her arm. The moment the needle touched her skin, Magic poured through his tiny body and exploded into the room through the small holes in the vents. The vents themselves were metallic, and conducted the magical energy rather than being destroyed by it.
Natasha and her attackers were not.
As the magic poured out into the room, it grabbed not only the attackers but also Natasha's lifeless corpse and did was Magic did best, it destroyed.
And as the magic tore them limb from limb, even the women he considered to be his mom, there was nothing Loki could do but watch. Watch as he broke them without meaning.
Later he would be told by Someone, Steve or Coulson or Thor, that it wasn't his fault. That she had been dead before the magic had touched her. That he wouldn't have been able to save her. That he was far too young to be expected to control such a powerful force.
He never believed them though.