(I'm assuming you're asking for the Utsuho gang? If not, lmk!)

Utsuho:

A good portion of the rainy day is spent experimenting with his bombs and poisons. After all, explosions and dust clouds don’t do well in moisture; how can he improve upon them in case the odds are ever turned against him?

The rest of the day is spent playing with Pochi and Uzume and giving Yakuma migraines with his usual mischief. You know, the usual.

Pochi:

If Pochi is out in the rain, a lot of their time will be spent looking for snails. It’s cute to watch, both the snails and Pochi.

There was one time where Neya taught them how to make a teru teru bouzu (see image), as a charm to pray for the rain to stop. But could it really be called one when it’s partially ripped, has thorns coming out of it, and has a face akin to a Lovecraftian horror?

Yakuma:

He spends most of the day collecting and drying herbs, concocting medicine, and nagging Utsuho like the good mother-doctor he is.

You might see him chasing after a wet Utsuho and Uzume with a towel.

Neya:

Her evenings are spent bathing a mud and rain-covered Pochi. She’s careful not to dunk any snails into the soapy bathwater. 

Any mollusks are tossed out the window. Somehow, they always land perfectly and safely on a leaf. Neya’s the gang’s best sharpshooter, don’t forget.

Hikae:

Rain? Snow? Sun? When you’ve lived for five hundred years, a change in weather is as significant as losing a single strand of hair. There isn’t much difference in what he does on a rainy day compared to what he does on a sunny day.

Unless it starts raining cats and dogs. He secretly hopes that idiom will actually come to life one day. 

Iwashi:

Iwashi is already meticulous as hell regarding skincare, but during the rainy season in June an extra ten steps are added to her beauty regime. The heat and humidity are gateways for sweat and acne, after all.

On raining traveling days, she’ll wear a fashionably modified version of a hikimawashi-kappa, or a waterproof traveler’s cape. If you ask her about it, she’ll happily style one for you :)

Uzume:

Don’t let him go out to play unless you’re okay with seeing (and cleaning) a Uzume caked with more mud than a swamp-dwelling alligator. 

Seriously, it’s already been an hour since you’ve started cleaning. How could there be more mud to clean off?

Chouza:

The bookworm (or scrollworm?) he is, Chouza can be found sitting by a window, listening to the rain as he reads.

There was a brief period where he thought the rain was beneficial as it would make his bangs stick to his face, covering his tattoos even more. But it resulted in Yakuma incessantly telling him to dry himself off so... Nevermind. 

Minamo:

Like Chouza, she enjoys meditating to the sound of the rain. There have been times though, where she was found napping instead. Maybe the rain was too calming?

If she goes outside, she likes to search for frogs. Just imagine Minamo with an umbrella in hand, curiously observing a small frog perched on a leaf...

(ugh, there goes my heart)

Tsukumo:

They’re part of the nature-appreciation trio with Pochi and Minamo. I’m not sure what creature they like the most, but they have a fondness for hydrangeas.

Oh, cool!  Translate is trying to learn things.  That’s the first time I’ve seen it say Choza on the blog...

But wait.  Let’s look at that one line a little more closely...

“However, I was eaten because my friends were not careful.”

Huh...

I'm not sure about you, but if I had to deal with a prankster who also happens to be a fucking genius I don't think I could get out of that without a headache LOL

(Ngl, my obsession for long haired 2D men started with Yakuma) Some headcanons regarding Yakuma and his profession:

As we all know, Yakuma’s mainly versed in Western medicine and its practices such as surgery. But considering how throughout the manga he’s been able to identify plants and herbs for consumption, it’s safe to say he’s also well-versed in pharmacognosy. 

I imagine he relied more on these herbal medicines for minor illnesses such as the common cold while traveling as they’re easier to obtain, process, and carry.

Since Yakuma didn’t get along with the other doctors at the imperial palace, much of this knowledge comes from self-studying. After returning from overseas, he spent much of his time reading up on books and journals borrowed from the library.