By now, whether Coulson could remember Tasidi's secret was no longer important.
Because Lena already knew. Whether the Death Warrior Project could succeed, and the key to reviving the dead, lay in whether souls could be brought back. The organization's previous research had likely kept failing because they had been unable to achieve that.
Still, Lena had used words to lure and deceive Coulson, making him willingly lie down on that machine and recall that now-unimportant past. The point was not the result, but the process. This was Nahash's test for her.
Nahash was a very powerful demon, though not as powerful as Mephisto. Therefore, if he wanted to remain active in the human world for a long time and complete his unfinished work, he needed a cover identity—possession.
But he was a snake with standards. It was not as though he would possess just anyone. He was not that indiscriminate!
It was like getting dressed. Of course one would want to wear comfortable silk and fine clothes. Who would want to drape tight, filthy rags over themselves?
And he thought Lena was quite suitable. First of all, she looked good. More importantly, they were highly compatible—both were consummate liars who spoke nothing but falsehoods. But seeing was believing, so Nahash decided to test her. He wanted her to break down Coulson's resistance, this strong-willed S.H.I.E.L.D. agent, through words alone and without using any coercive methods.
Lena had no choice but to comply. Although becoming a demon's vessel did not sound like a good thing, she had no alternative. The moment Nahash appeared, he slaughtered everyone in the room, leaving only her alive. He had probably noticed that she had the potential to become a catalyst.
If she refused, or lost that value, she would likely follow in the others'