It's obvious from the context that the subject/speaker is inside of the office, and the water is outside of the window, so 滲み出ている has the same meaning as 滲み出てきている there.
I previously think we can't use〜送ってきている here because いつからそこにいたのか has established that the reference point in time is past and the action 送ってくる started prior to the the reference point in time. In this context, by the time 士道 found that 十香 was there, 十香 had already given him an anxious look. Does it make sense?
Thank you. Yes, I know that flow of description is unnatural because all the sentences end with た form. So whether the ていた form is used or not doesn't depend on the start point in time of the action but we just mix the tenses so that the ratio of the た form to the る form is close to 1:1. As simple as that?
So whether the ていた form is used or not doesn't depend on the start point in time of the action but we just mix the tenses so that the ratio of the た form to the る form is close to 1:1. As simple as that?
are not the same. There are reasons why 振り向く and 送ってきていた are used there at least for the author. (Needless to say, there are cases where only the present or past form can work well by grammatical necessity, of course.)
The following site explains an effect to use both present and past forms relatively well (a bit long, though). 小説の書き方講座