This is the process of a character being pressured, indoctrinated, or subtly forced to change their ideas and beliefs. It can be inflicted by an individual (an abuser, for instance) or a group (in the case of a cult), and the victim is often unaware that their adapted outlook, attitudes, and behaviors are the product of manipulation.

Adopting new habits or rituals related to their dress, diet, religious practices, etc. 
Following a routine that is different (and more restricted) than it used to be
Attending regular meetings, gatherings, or retreats
Complying with rules and demands 
Using new words or terms that are cryptic or not widely known
Giving up hobbies and favorite pastimes
Spending less time with loved ones
Pulling away from old friends
Missing days at work or school
Abruptly breaking off contact with people
Moving out of a home shared with family members
Keeping to themselves in the workplace
Talking incessantly about the person or group doing the brainwashing
Proselytizing; trying to get friends to join the group or embrace their way of thinking
Questioning or criticizing ideas and beliefs the character used to embrace
Getting frequent texts or phone calls the character is compelled to respond to right away
Blindly agreeing with and following the tenets of a group or group leader
Exhibiting co-dependent behaviors
Giving money, possessions, and anything else requested to the group or individual
Using drugs supplied by the brainwasher
Signs of exhaustion (dark circles under the eyes, staring blankly, poor skin tone, nodding off during the day, etc.)