事(こと)になるIt will end up being, It is the result of, It has been decided that

Both にする and ことになる relate to decisions but differ in agency. にする is used when the speaker actively chooses something, often in daily situations like deciding what to eat, similar to 'I'll go with X.' ことになる, on the other hand, expresses decisions made by others or by circumstance, like saying 'It's been decided that X.'

These expressions are similar in that both are used to express decisions. ことになる conveys that something has been decided or will happen due to external factors, e.g. 来月転勤することになった ('It's been decided that I'll be transferred next month'), while ことにする describes something the speaker has decided of their own power, e.g. 来月仕事を辞めることにした ('I've decided to quit my job next month').

These are closely related patterns with a slight but clear nuance difference. ことになる expresses that something has been decided or will happen, often beyond the speaker's control, e.g. 転勤することになった ('It's been decided that I'll be transferred'), while ことになっている is typically used to refer to an established or habitual rule, e.g. 会議を行うことになっている ('It's been decided we'll hold a meeting').

These patterns are related in that both center around the idea of something being decided. ことになる expresses that something has been decided or will happen, often beyond the speaker's control, e.g. 転勤することになった ('It's been decided that I'll be transferred'), while に決まっている expresses that something is decisively true, e.g. 勝つに決まっている ('They'll definitely win').

Both ようになる and ことになる express something becoming a certain way, but with different nuances. ようになる describes a change in state, e.g. 話せるようになった ('I became able to speak.') ことになる, on the other hand, conveys a decision made, often outside the speaker's control, e.g. 辞めることになった ('It was decided that I/he/she would quit.').