Can I use "ee" instead of "hai"?

Question of the Week Vol. 8

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This week's question is "Can I use "ee" instead of "hai"?

Both "hai" and "ee" mean "yes". "Hai" is formal and "ee" is casual (used in daily conversation). There are some situations in which "hai" can not be replaced with "ee."

(1) When your name is called (taking attendance etc.)
 

Tanaka-san.  
田中さん。
Mr. Tanaka.
Hai.
はい。
Yes, present.


(2) When answering the phone.

Hai, Kimura desu. 
はい、木村です。
Yes, this is Kimura.


(3) When answering your door.

Hai, douzo.
はい、どうぞ。
Yes, please (come in).


(4) When you respond to someone's request.

Hai. 
はい。
Yes (I will do it).


"Un" is also used as "yes". It is very casual, therefore used only among family members or close friends.