Which hot springs are ok for tatoo in Sendai?

I am going to go to Sendai next month.
Are there any hot springs that I can go to with tatoo on?

You are hardly the first person to ask this. You can look through a few sites that share this information, like
https://en.tattoo-go.in
https://tattoo-friendly.jp
Though for some ryokan or hotels, they might only allow you in if you are a staying guest there.