Throughout the world, セイン (Sein 
, Thain 
, Thane 
) is a common mostly boy's, but seldom female given name. The forename セイン is habitual in Mongolia, where it is a common predominantly boy's, but very infrequently girly name, New Zealand, where it is quite a common male name, and Myanmar, where it is quite a rare mostly male, but infrequently girly name. Not in comparison with a country's population, it is commonest in Mongolia, New Zealand, and the United States. Also, セイン is the last name as well as the forename.
セイン is also a name for the fictitious and mythical characters: Thane Krios , the fictional character in the Mass Effect video game series; sein Vetter , the operatic character in the operetta Abschiedswalzer; Sein Jünger , the operatic character in the opera Der Golem; Sein Sekretär , the operatic character in the opera Der junge Lord and Sein Schneidermeister , the operatic character in the opera Kleider machen Leute (Zemlinsky), among other works.