Rakuten referral bonus

Yes. U.S. citizens and residents are taxed on all worldwide income, whether they received a Form 1099 or not.

To report your referral bonus:

1. Click Federal in the left column
2. Click Wages & Income 
3. Scroll down to Less Common Income. Tap Show more
4. Select Miscellaneous Income, 1099-A, 1099-C
5. Select Other reportable income
6. Say Yes to Any Other Taxable Income?
7. Enter a description (Rakuten referral bonus) and amount ($120)

That's tricky.

If we view the commissions as discounts, they are not taxable.  "Normal" credit card cash back deals are not taxable because it represents a discount or rebate of the merchant fee charged by the bank to the merchant, and rebates or discounts are not taxable, they are just price reductions. (Of course, if you use the property in business, you must use the reduced or net cost.)

However, to the extent that the merchant is paying Rakuten for advertising, and Rakuten pays part of that to you, it's not a purchase discount, but a commission, and I think it would be taxable.

Since I don't know exactly how it works I hesitate to give a strong opinion, but your cash back probably is taxable. 

Referral bonuses are definitely taxable because there is no way it could represent a discount on something you purchased.