[quote=@Raineh Daze]
<Snipped quote by Letter Bee>

... do you want to die [i]post two?[/i] 
[/quote]

Not really, it's just that it would be in-character for Osamu to assume the worst upon seeing Elizabeth, and try to do something about it.

Remember, Osamu's job is to keep the masquerade going, and interprets it as keeping civilians from being involved in ways that harm them.

Hmm, perhaps Osamu can, instead of just shooting at Elizabeth, call 'The Moon', aka the Mage's Circle in Japan, in order to ask for any data on Elizabeth?

Edit: True, Osamu might not be able to distinguish between a tryst and a vampirization.