You decide to stalk one of your brother's usual hangouts waiting for him to show up.
When you finally see him show up, you flag him down and call him over. As he greets you, you grab his hand and activate the device. You proceed to drain his manliness, you feel your clothes get tighter as your body becomes more muscular and manly. Your brother's features on the other hand become smaller and more delicate;
by the time you are done your brother looks beyond androgynous he looks outright feminine but the device clearly states that he is still male.
He tries to protest but you tell him to shut up. Much to your surprise he doesn't protest and immediately obeys. You try giving him a few more commands all of which he obeys. Seems that along with his masculinity you took all of his assertiveness, leaving him completely submissive and unable to disobey a command.