“Mwaramutse” is used for “Good Morning”. It is used for someone you mostly see often. It is used until 10:00am or noon.
The response to “Mwaramutse” is also “Mwaramutse”. Sometimes people will add “ho” to respond “Mwaramutseho”, which is still the same thing.
Just like Muraho to Uraho, you can also say “Waramutse” instead of “Mwaramutse” when addressing to one person. This is rarely used too and it’s informal.
Normally you will use “Mwaramutse” when addressing to many people, or one to sound respectful