Thankfully my girl Manatsu is really open and straightforward, so I trust she will be able to muster her courage on day seven and ask Nagi to add an extension to their deal, maybe indefinitely :)
It's so sweet that Manatsu keeps doting on Nagi, and that it's absolutely working. Other people might be bothered by Nagi's aloof disposition but Manatsu treasures every small reaction she can get out of Nagi.