Purple Heart or Purple Sister

He has a rather complex device that looks like a VR gaming helmet he can use

On one hand he could send it to Neptune as a new up coming VR gaming helmet for her to test out

Once she uses it he can override her consciousness with his own

The downside here is that others will notice that Neptune has become different especially Neptune's younger sister, Nepgear

So he'll have to avoid others and use that method to acquire Neptune's memories before he interacts with anyone

Annoydeath is certain that he can be a better big sister for Nepgear than Neptune herself

On the flip side, he could send it to Nepgear

With how easily everyone seems to forget her it'll be extremely easy to get her memories and behave as her

Plus her love and understanding of technology is the perfect counterpart to his love and understanding of coding

AND since she is the CPU Candidate of Planeptune in her dimension, it's more than likely that her cute CPU form would get a sexy upgrade once she takes over as CPU