Because this Unit only requires an extra 2000 Power to use its effect all the time, it is more versatile than Enigman Storm. The downside is that it can't be searched, and it tends to be crucial in a deck revolving around it.
Miracle Beauty, Masked Police, Grander, Guide Dolphin and Cosmo Roar are all excellent cards to use with this. Miracle Beauty can get more mileage out of Stands, be it triggers or Rain's effect. Grander, Dolphin and Roar can all easily activate Rain's skill, and Roar synergizes with the Stand theme, while Guide Dolphin is a Stand trigger itself.
Enigman Rain also works with Commander Laurel (however, it is advisable to not have Grander as the main source of powering up the Vanguard in a deck utilizing Laurel. Instead, you can use Cosmo Beak for the additional Power which helps guarantee your hits more often). Even if some of your Units are rested, when Rain hits, you can Stand them (especially works with Miracle Beauty and Cosmo Roar) and then use Laurel to Stand Rain, quite possibly repeating the combo. With 2 Stand triggers amongst 2 Twin Drives, and 2 Miracle Beauty on the field, it is possible to use Laurel's effect twice in a single turn, although highly unlikely.
Boost this Unit with Karenroid Daisy - with the extra 2000 Power from the aforementioned sources, this will enable Rain to reach 20000, which is a reasonable offensive Power. Alternatively you can use Glory Maker, which will require at least 20000 Shield to block safely by anything except Cross Rides and Knight of Fury, Agravain.