Cheat: There's a big rock outside of Grandma's house over at the very top right corner of the map. Inspect it to have a prompt show up, then mash as many times as needed. The hint is a reference that in Animal Crossing, one of the easiest ways to get money is by hitting rocks.
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Easiest way to cheat in RPG Maker games is still the
RPG Maker MV MZ, CheatMenu
The rock gives you each time lile 50 Yen, with Cheat Menu you can give yourself directly 99999 and also look for items, HP etc. values.
EDIT:
If someone is going to use the Cheat Menu, I've found variables for girls progress and MCs HP.
Look under "Variables" to find them.
(See Screenshot attachment)
EDIT2:
Progress variables are:
Fuyu: "進行度:制服姉"
Emi: "進行度:売店姉"
Honoka: "進行度:巫女姉"
Increase the variable each time by 10, then get the event done to progress.
HP: "体力の現在値"