Sekai 

Japanese for "world"

This sekai is filled with water, vegetation, and life.

Sekai by The SF Kid March 10, 2013

Sekai 

Ship name for EXO's Sehun and Kai. One of the most best ships that graced the earth. These two are engaged.

Sekai is engaged???

Yes Kai gave Sehun a pink heart-shaped ring.

Sekai by HunJonginnie July 9, 2018

Sekai 

The name for a female who is lit, sexy af, and fine as hell. She is also straight up about how she feels. Has a big ass.

Damn Sekai is sexy af.
She has a big ass.

Sekai by Dsdfererntjymky,ut,U.K.,yr January 14, 2017

Sekai 

THOT from School Days

Sekai Saionji? What a whore. Slut. Bitch.

Sekai by suck_my_d33 June 28, 2021

Sekai 

A space created by a human's true emotions, attached to song.

Miku: Welcome to MEGA Sekai

Person: Woah, I created my own sekai!

Sekai by retropaz August 3, 2022

Sekai Ichi 

Japanese for "World's Greatest", or "Best in the World".

"BAKAMONO GA! DOITSU NO KAGAKU WA SEKAI ICHI!"
"You utter fool! German science is the best in the world!"

Sekai Ichi by Arky the Returd January 14, 2020

Sekai-Ichi Hatsukoi

Sekai-Ichi is a manga and anime by the author Nakamura Shungiku, who is famous for writing the anime and manga Junjou Romantica. She is a yaoi or boys' love author. Some of her other creations are √W.P.B. (2003)
Castilla (2000)
Hybrid Child (2005)
Junjou Mistake (2008)
Junjou Romantica (2002)
Junjou Romantica Artbook (2008)
Junjou Romantica dj - Chika*Chika 3)
Mangetsu Monogatari (2009)
Picturesque of a Mask (2004)
Restaurant Games (2003)
Sekaiichi Hatsukoi (2008)
Touzandou Tentsui Ibun (1998)
Tsuki wa Yamiyo ni Kakuru ga Gotoku (1999)
Umi ni Nemuru Hana (2001)
In the Sekai-Ichi Hatsukoi manga and anime, Usagi Akihiko is mentioned, as he is a character in her series, junjou romantica.

The ukes in Sekai-Ichi Hatsukoi are so cute!

The whats, in what?
Oh, never mind. You won't get it because you don't like yaoi.

Sekai-Ichi Hatsukoi by Moki-Chan November 13, 2011