Yuu Tosaki is a high-ranked member of the Ministry of Health, Labor and Welfare.

Generally, Tosaki has a commanding air about him and wears a serious expression. His answers are always short and to the point. He is also quite blunt and lacks patience.

He's quick to anger with certain triggers, such as multiple instances in which he snaps at the mispronunciation of his name - "Tozaki" as opposed to what he claims is correct, "Tosaki".

From the very start, Tosaki is shown to be morally ambiguous. It isn't above him to resort to violence through either his own force or those beneath him to get something done. If the consequences of his actions don't have a direct effect on him, his reaction is mild at best.

Tosaki relies heavily on Izumi Shimomura to protect him from the Ajin and their IBM with her own abilities, threatening her with the prospect of being locked up and experimented on if he dies.