The first Chu Rat can be found near a group of smaller, weaker Shiyou Rats, which closely resemble it and do not run from Tingle or attack him. The Chu Rat drops the one Bone when defeated, the same amount as a Shiyou Rats, but it drops more Rupees as it deals more damage.
When Tingle arrives at Sunshine Shore, Aba continues her Battle Class and will place several Chu Rats for Tingle to battle. First she has Tingle fight one of them, and then has him group five of them together and fight them at the same time.
There is no known official name for this enemy, but in the game files, it is called "Rat_2."