koto ni naru) indicates something that has been decided to do by circumstance. Some cases in which ことになる is used can be:
The conditions changed so that a certain action was allowed to happen
The external situation evolved independently of one's will and a decision was therefore made
After a discussion it was decided to do that thing
These are mostly plans and decisions that developed independently of one's will
ことになる is the opposite of ことにする: with ことにする (
koto ni suru) the action one performs is for a decision made by oneself directly.
In Japanese there are numerous expressions with the noun こと (
koto) which means
こと is a noun, so it follows the same rules of all nouns:
It is preceded by a particle or a verb
Comes followed by a particle
The verb なる (
to become and is used in various plain or polite forms, affirmative or negative depending on the circumstance:
Examples of ことになる in Japanese
I will move to Rome.
The meaning is
It has been decided for my transfer to Rome or
For various reasons I will be transferred to Rome. Specifically, the decision was taken by someone else and not by me directly.
From next month I will go to China for work.
Also here, the meaning is closer to
It has been decided that I go to China for work (I did not choose it).
It is possible to use the mobile phone instead of the dictionary during lessons.
The event scheduled for next week has been canceled.
In this example we can see that ことになる expresses a decision that was caused by external conditions that are outside of our direct control. Evidently there were some difficulties and it was decided to cancel the program.
ことになる in everyday life
In the first panel, the girl is imagining what she will do on her day off from work.
In the second, she receives the call to change plans and is asked to apologize for working on the day off.
In the third and final panel the sentence is:
I'll go to work tomorrow.
The decision of going to work at the end was not taken by her boss. The nuance is "for a non-personal choice", for a problem that occurred at work, for an unexpected and change of plans at work ... I have to go to work tomorrow.