This trip required a ton of planning, that totally paid off. So, I'm sharing the itinerary in full bullet form (instead of prose with photos) for easy sharing with friends.
I hate to admit, but it helped a bit with overnight stays that we were only four (the oldest had a different spring break and stayed back in Tokyo). So, rather than our usual "sleeps five," this visit was only four.
We drove our car the whole way. Tolls one way to Kurashiki were about Y14,000 (and a shinkansen unreserved day of ticket is Y16,000 ... so multiply that x4, plus a rental car for when on Shikoku, and that got pretty pricey).
Day One
By 0800, Depart Tokyo for Kurashiki
8 hour drive (alternative: shinkansen to Kurashiki, rent car on Day 2)
Walk around Kurashiki Historical District
Note - dinner places there were slim. Many more options near the train station
Arrive Kurashiki Ivy Square (overnight) (via Booking.com)
Day Two
0800, Depart Kurashiki Ivy Square
30 minute drive over Seto Bridge
See Marugame Castle
The visitor center had a fun fan making class (takes about an hour). Usually requires advance reservations (not sure how… I talked my way in)
Eat early lunch or pick up food for lunch
1100 - Drive to Iya Valley (~2 hours) https://www.iyatime.com/
Iya Sites: Oku Iya vine bridge, Peeing Boy statue, Scarecrow Village
Overnight in Traveler’s Inn Nakone (cast Y40,000 including Iya-style kaiseki dinner and breakfast). (Futon room could sleep five)
Address: 徳島県三好市西祖谷山村榎242 Nakamoto-san 090-8692-9055
Tokushima-ken, Miyoshi-shi, Nishi Iya Yamamura 242
Back up options: Hotel Obokekyo, Iya-no-yado
Day Three
0900 - Iya Forest Adventure zipline (cash Y16,000)
Make reservation online ahead of time https://fa-iya.foret-aventure.jp/eng/
1100 - two hour drive to Kochi Castle
See Kochi Castle
Lunch at Hirome Market (hawker stalls - eat in or take picnic to castle)
No later than 1600 - three hour drive to Forest Cottage 高知県四万十市西土佐奥屋内1071-3
Pick up food in Shimanto City for dinner (2), lunch, breakfast (2)
Stop at coast along drive
1900 - Forest Cottage (overnight) (credit card payment at house) (space for max five to sleep)
Confirmed - tel:0880-56-1229 / e-mail:morikote@mb.gallery.ne.jp
Day Four
0900 - Workshop Kurogane knife making activity (cash for two knives Y32,000)
Confirmed - tel: 0880-54-1811 / Email: (not sure - I called)
https://visitkochijapan.com/en/activities/10159
1700 - workshop ends
Backup: check out Shimanto River guide for boat tours: https://www.shimanto-kankou.com/pdf/english2.pdf https://www.shimanto-kankou.com/
Overnight in Forest Cottage
Day Five
TBC - 1.5 hour drive to Uawjima Castle
See Uwajima Castle (opens 0900), big snack or lunch?
TBC - 1.5 hour drive to Matsuyama
Late lunch or snack in Matsuyama
See Matsuyama Castle (open until 1700)
If time, go see Dogo Onsen (ride on street car)
Overnight in Comfort Stay Matsuyama (via Booking.com)
Day Six
Depart for Tokyo (~10 hour drive)
(or drive back to Kurashiki to return car and take shinkansen)