The summer training camp starts in Early July(7 月前半) in the second and third year. Tazuna will tell you about it two turns ahead of time. Rest up and try to have full energy and mood going in. Ideally all your supports will have high bond and be able to rainbow, too.
During summer, all of the trainings are increased to Level 5. So, while it’s a good time to get big rainbows, it’s also the perfect time to fix your stats that are falling behind. If you’re missing stamina, guts, or wit, you can gain a lot of it quickly during summer.
The infirmary in the summer camp can’t fix all illnesses, only some of them.