Sacchan shows Yui an item she found that had fallen into their secret hideout:

Sacchan: 「変(へん)なメガネ」

The noun 変(へん) (weird) is a modifier for メガネ (glasses).

As a basic sentence, 「メガネが変(へん)だ」 (the glasses are weird) uses だ as a coupler. When the descriptive noun 変(へん) is used to modify メガネ, this だ becomes な.

Since their family’s trip to the aquarium was cancelled, Kanami’s older brother bought sketch books and crayons for an alternative activity to cheer up his sister.

Brother: 「これにお魚(さかな)の絵(え)描(か)こうよ」

He suggests the two of them draw 絵(え) (pictures). This word is modified by the noun お魚(さかな) (fish), to suggest they draw pictures of fish. The modifier の is used to separate the nouns.

After being late to school, Usagi is told to stand out in the hall. There, Usagi laments her situation.

Usagi：「んもーーっ　か弱(よわ)い女(おんな)のコを廊下(ろうか)に立(た)せたわねっ」

She says to herself that an か弱(よわ)い (cute fragile) 女(おんな)のコ (girl) shouldn’t be made to stand out in the hall. Here, the adjective か弱(よわ)い modifies 女(おんな)のコ.