(watch out for spoilers in this text!)
Kaworu Nagisa (渚 カヲル Nagisa Kaworu) is a character from Neon Genesis Evangelion. His true sexual identity remains unclear due to several different reasons, one being the fact that he´s not exactly human himself, so it´s unclear if human terms of sexuality even apply. Another reason is the fact that he never really comments on his sexuality or what he identifies as.
He is, however, actively trying to hit on Shinji by touching him, making compliments, being comfortable with nudeness around him, inviting him to alone time together, sharing a bath, having a sleepover, even telling him that he loves him.
Kaworu has different appearances in the different versions of the story. He always appears to be somehow morally grey and is a highly ambiguous character. From a plot perspective, his entrance into the story means bad news. At the same time he´s the one person who´s getting the strongest emotional responses and the most intense connection to the main character in the shortest time possible.
There is fandom discussion about his true motives and whether or not he actually loved Shinji, because the meeting of both characters always causes severe trauma and leaves Shinji emotionally and psychologically shattered when he ultimately decides to die by Shinji's hand in order to allow humans to live on.
However you choose to interpret it: Kaworu plays an important role in Shinji´s coming of age aspect of the story. He makes him experience an unexpected but obvious male crush: Shinji blushes at almost everything Kaworu says, he agrees to every suggestion Kaworu makes, he even readily agrees to share a room with him overnight, even though physical contact seemed to have dubious consent from Shinji´s side until then. It´s implied that Shinji could be open to romance and, yes, even sexual experiences with him. This consent is given nonverbal though and their scenes on screen remain platonic.