Kdrama where main leads switch to banmal?

Amost every drama has it :D

There are too many for me to remember, so I really can't name them but really a lot of them has it :)

Lol, if u watch high school dramas everyone is using banmal :)

Banmal is not spoken only because they are classmates but because their age is same.

I checked your bio and u are older then me which means I would NEVER dare do use banmal with you, but rather call you eonnie. Switching to banmal is a huge step, but the most obvious is for now I think Fate and Furies maybe? In first episode the main guy used banmal towards the heroine but then switched back to formal one to show her, that he respects her. 

I think Legend of the blue sea also has it, and it's not a high school drama...

But I think Min Ho used banmal from the start....

Really I don't analyse it that much :D

Sorry to ask, but I am really curious, what is Banmal and  jundemal  ?

 Azalae:

Sorry to ask, but I am really curious, what is Banmal and  jundemal  ?

So in the Korean language there are different ways of addressing people based on their age and or status. It's called the honorific speech system. Korea, and Asia in general, adhere to a hierarchical system in which everything that's bigger (in number, in age and in status) must start or be placed at the top.  Even the way they write the date is hierarchical: 2019.01.21. The higher up on the hierarchy a person is, the more you need to use formal speech.

So simply put, Banmal is the least formal mode of honorific speech and is reserved for very close relations - family members (parent/child, husband/wife, siblings) and close friends or lovers who are the same age. However, this isn't always a given as sometimes even family members use Jundemal (formal speech) with each other. It all depends on context & a number of other factors - your age vs the other person's age, your status vs the other person's status, the closeness of the relationship, the situation (if you're in a formal setting then younger family members or close friends might revert to Jundemal to show respect for the hierarchical order of things). Lovers can speak Banmal to each other, but the younger party may still refer respectfully to the older party ... so the girl may call the guy 'oppa' or the guy will call the woman 'noona'.

Usually people should invite you to use Banmal with them, rather than you taking it up on yourself to use it without invitation/permission. Using Banmal with someone, esp a stranger or someone older who did not personally invite you to 'speak comfortably' with them, can and often is seen as massively disrespectful. This can occur even with family members.

The line for when it's acceptable to use Banmal can be very blurry, so to avoid any misunderstandings most people will always start out using Jundemal until they're invited to use Banmal.

So where Banmal is informal speech, Jundemal is formal speech which is meant to show respect and is reserved for anyone who is not a close family member or very close friend/lover who is the same age as you.  Jundemal in itself appears to have 3 distinct levels, which is meant to indicate the DEGREE of respect you're trying to show the person:

When someone uses 'YO' at the end of their words - this is the most basic form of respect and is generally accepted as the standard to use for & with everyone, esp strangers who you don't know anything about. If you use 'yo' to address people, no one will get upset at you. It's the most universal form of honorific speech.

nimida/simida is a notch above 'yo'  - you may use this in situations where you want to show above average respect to a person, so for eg boss/employee, teacher/student settings or between merchants and clients/customers etc.

simikka / sippchiyo - is the highest form of honorific speech & is mostly reserved for nobility or people with super high statuses, eg presidents, company chairmen and so on.

You decide which form of Jundemal to use depending on the amount of respect you want to show the person.

Someone who works for you may be way older than you, but they still must use Jundemal because of your status. You - even with your high status - should always use Jundemal in every situation, but esp if your employee is older than you. Some people with high statuses, however, will resort to using Banmal as a sign of disrespect toward their workers or people who they see as 'beneath' them.

I'm learning Korean so this is what I've deduced from studying the language and, of course, watching dramas, but I'm by no means an expert ... so people should correct me if I've said something wrong here.