Why the yuna'sRelationship can not ncreased after 40.l have been tried do long.
You need an event. I forgot which one. I think its buying her running shoes in syn's shop
Once it becomes night, you need to talk to Yuna, click on "gift" and select the "talk" option. Yuna will reveal that she wants to start running but doesn't have running shoes, giving you your new objective.