Reactive power always flows out and back; they are just making it clear that it has to be accounted for.
The bidirectional arrow labeled real power indicates that real power may be drawn from AC 1 or 2.
Hello! thanks for your response. Could you please answer to my following question?
There is only one bidirectional arrow at the transformer near AC1 & AC2 which indicates reactive power can follow in and out the transformer. Can I add one more bidirectional arrow at the transformer to represent real power follow? Because I think, not only reactive power but also real power is following in and out the transformer.