Rounders

The 'Rounders' are a fictional team of mercenaries that appear in Steins;Gate, and act as the series' secondary antagonists.

While they are, at first, believed to be working for SERN, they are soon revealed to be an organization that are working independently from them. Unlike SERN, who carry out the actual research, the Rounders operate in the shadows, carrying out tasks such as assassination in their stead.

Despite their appearance, the Rounders are well-trained professionals, showing the ability to infiltrate and overwhelm Akihabara in a matter of hours. Their professionalism is further shown through many different ways, most notable of which being that they were able to prevent entry to and exit from Akihabara via an un-official vehicle search, as well as being able to follow Okabe and render him unconscious without being noticed until the very last moment.

Aside from the above information, not much else is known about them.