The ad's crossover theme matches a tote bag bundled with 14th tankoubon of 3-gatsu no Lion, the events depicted in the ads occur after the 2nd season and contain some spoilers.

Hinata Kawamoto see two girls carrying rabbit-print tote bags. The girls are none other than Hagumi Hanamoto and Ayumi Yamada from Hachimitsu to Clover. Hinata immediately runs home and then to the bookstore to buy a copy of the 14th manga volume to receive her complimentary tote.

In a second ad, Rei Kiriyama is coaching the team in shogi at Fujiwara Design.

(Source: ANN)