Tropes for this episode include:

Ancient Evil: The Spirit Tortoise is described as a cyclical monster that brings great disaster whenever it manifests.
Hard Work Hardly Works: Itsuki's party seem to be under the assumption that because Rishia is weak now, that means that she will never improve and that she should just give up and go home. Though in Itsuki's case, it's still left rather vague if he really thinks that or if he's doing it for her own protection.
Hypocrite: In the first season, the Sword, Spear and Bow Hero were perfectly willing to perform acts of grandiose heroism. Here they turn the Queen down when she asks for help fighting the Spirit Tortoise, claiming that it's outside their job description in fighting the waves. If they turned it down because of how badly they screwed up last time (Motoyasu causing an infestation of plant monsters trying to stop a famine, Itsuki plunging a kingdom into poverty after killing its tyrannical king, Ren causing a pandemic after slaying a dragon), none of them mention, nor imply it.
Pragmatic Adaptation: The anime skips over the Training arc that introduced Eclair Seaetto and Elrasla "Granny" Grilaroc's Ki Manipulation fighting-style, both of them already helping train recruits for future Waves.

Recap / The Rising of the Shield Hero S2E1 "A New Roar"