に: the target — where to, when, and to whom
The place you go to, the time something happens, where something is, who receives.要点The idea
に points at a target: the place you're going, the time something happens, the place something is, or the person who receives.学校がっこう に 行いく。gakkou ni iku.I'm going to school.A destination.
七時しちじ に 起おきます。shichiji ni okimasu.I get up at seven.A point in time.
猫ねこ は 部屋へや に いる。neko wa heya ni iru.The cat is in the room.Where something is.
友達ともだち に プレゼント を あげた。tomodachi ni purezento o ageta.I gave my friend a present.Who receives.
A友達ともだち に 手紙てがみ を 書かいた。tomodachi ni tegami o kaita.I wrote a letter to a friend.The friend receives it.
B友達ともだち と 手紙てがみ を 書かいた。tomodachi to tegami o kaita.I wrote a letter with a friend.The friend wrote it with you.
Time and destination together
日曜日にちようび に 東京とうきょう に 行いく。nichiyoubi ni toukyou ni iku.I'm going to Tokyo on Sunday.Two に: one for the time, one for the destination. Time tends to come first, by habit rather than rule. In casual speech a day like 日曜日にちようび can drop its に; a clock time keeps it.
Purpose and change
公園こうえん に 遊あそび に 行いく。kouen ni asobi ni iku.I'm going to the park to play.The ます form minus ます (遊あそびます → 遊あそび) + に + go/come = go/come in order to do something.
水みず が 氷こおり に なった。mizu ga koori ni natta.The water turned into ice.に marks what something becomes.
- A夏休なつやすみ に どこか 行いきました か？natsuyasumi ni dokoka ikimashita ka?Did you go anywhere over the summer holidays?
- Bはい、 京都きょうと に 行いきました。hai, kyouto ni ikimashita.Yes, I went to Kyoto.
- Aいい です ね。 誰だれ と 行いきました か？ii desu ne. dare to ikimashita ka?Nice. Who did you go with?
- B家族かぞく と です。 祖母そぼ に 会あい に 行いきました。kazoku to desu. sobo ni ai ni ikimashita.With my family. We went to see my grandmother.