I have two questions about it.

1) Can I put a character with "no attachment" ?

2) If the card attached by it should be revealed for it's rationality ?

Cards in shadows are not in play (shadow rules) and they have no other characteric than "card in shadows" (FAQ section 4.16), among others, no text, including keywords.

You do not to reveal the card before you bring it out of shadows or the game is over (tournament rules require all cards in shadows to be revealed at the end of a game), any more than you reveal regular shadow cards. If you really have a reason to think your opponent could make a mistake (or even cheat), call for a judge to check.