Reimu Hakurei = Philip Marisa Kirisame = Shotaro Hidari
Reimu is merely the personification of the Heat Memory (since the Heat Memory is red and Reimu's clothes are mostly red), while Marisa is merely the personification of the Metal Memory (though the Metal Memory is silver and Marisa's clothes are mostly black).
The H on Reimu's half may be "Heat" or "Hakurei", while the M on Marisa's half may be "Metal" or "Marisa".