.. Serge's nickname

You have the ability to listen to the past, don't you?

Try it on items.

Have you continued your conversation with Serge? Summon him back, again. Inquire him about the book. He will write impressions in to the book. Give him some long prose.

But did you spot what he left behind? ( On the table. )

The pen is on the table. Use the Haunter's Mark on it.

Now you know the nickname. You better tell Serge.