Delayed return to Toyoko Inn, email?

I left Toyoko Inn in Tokyo and told them I would return next day as I have a reservation there then. But due to circumstances I might not be able to return to Tokyo tomorrow.

What will they do about my luggage? How to contact them saying I probably will not return until the day after? Calling might be hard to explain so they do not misunderstand.

I have pre paid the reservation so they ought to know I will return eventually

On the receipt it says return for check in tomorrow.

Try calling them first. You might get lucky and an English-speaking staff may be there.
You don't want them to cancel your reservation if you are arriving one day later.

If I cancel the reservation and there is a reservation for the next day, you mean they might cancel the next day even if today is cancelled by myself?

Yes they will probably cancel the whole reservation if you don't show up the first day.

So best to call them as suggested. No more wasting keystrokes here.

Usual terms for a no-show vary from charging one day through to cancelling the reservation and charging the full stay. As you mention, your booking is pre-paid. Call or write to them direct.

If no one can assist you, make your phone call, and if they don't speak your language, say,

"Sui-yo-bi ni modori-masu." (I will return on Wednesday.)

Have tried to aquire a phone during the day but with bad results, tbh the reservation is cancelable until early evening for Toyoko Inn, not that I want to abuse it though.

The reservation is made in several different bookings, one each day, so I find it hard they might cancel all days. Noticed they had written 2/12 in the note, and c/I. Thought they noted the c/i date.