1. Used to refer to your older brother in a cute way (in japanese).
2. In hentai, mostly lolicon, the lolis use it to refer in a cute way to their lover.
3. Cringey term that lots of weeaboos use to refer to their crushes.
1. Onii-chan, watashitachiha shukudai o shinakareba narimasen. (Onii-chan, we have to do our homework.)
2. Onii-chan, daisuki! (I love you, onii-chan!)
3. Len onii-chan is so cute! He's my shota! Kawaii!
Means big brother in japanese and not used in any type of sexual or romantic way. It just means big brother in japanese.....chan here refers to the formal greeting that any kind of people use it to refer it to the elders where onii means big so in total it refers to big elder or big brother.