Kaworu turns the ball in his hands thoughtfully, wondering how he ought to deal with this. If Asuka doesn't continue to insist for further explanation as to why he has that weapon, it's probably best that he not offer it. At the same time, she could start to understand what he meant when he asked for her to forgive him. Although Kaworu doesn't know the details of what happened after his death, he had a fairly good idea of what must have occurred, between what he already knew about Seele and what Asuka had mentioned here and there.

Kaworu knew now that Eva series had always existed for the purposes of starting Instrumentality. He underwent simulation training with a similar weapon just to supply adequate dummy plugs for them. If Asuka recognized the blade, it means she saw those Evas first hand. His Evas.

"They were deployed by Seele when NERV was attacked," he said calmly. It's an ambiguous statement; both a request for her confirmation and an acknowledgement that it likely happened.