Meaning of “Sekaisen(世界線)”

“Sekaisen(世界線)” means kind of parallel world.

In my image, this word was getting popular because of an Anime “STEINS;GATE(シュタインズ・ゲート)”.
This anime is from video game, I’ve never played it, but the anime is so great.
I recommend to watch it!!
If you watch it, you can understand the meaning.

These days, this word become an almost common word not only for otaku.

Example Conversation

A: Oh? You are a classmate with her, aren’t you?
B: No, I’ve never talked with her. Are you talking about in another Sekaisen?
A: Hmm… misunderstanding…?

A: あれ、お前あいつと同じクラスじゃなかったけ?
B: 違うよ、しゃべったこともない。どこの世界線の話してんの?
A: あれー、勘違いなのかぁ

>> ASK ME about Japanese something!