I trying to book car from Tocoo, total hours about 20hrs.
Why is there a charge of TAS for 2 days?
Do I need a ETC card in Izu?
The fee you mentioned is probably calculated over a 2-day period (you will have the car for 20 hours, thus crossing two calendar days).
You don't need an ETC card. Just pay cash at the toll booths. There are hardly any meaningful discounts these days.