ain't that tagalog? das the wrong translation, isn't it?
Algester said:
mabuhay is itself hard to translate into english... since its more or less used as a courteous greeting
From my understanding it means "long live the..." (literally a command to "Live!") and is used during events and rallies to exult someone or some entity (or to toast someone when drinking). This makes it pretty much identical to Spanish "Viva...", and similar to Japanese "banzai".
...But recently (well, starting in the nineties) it has also been co-opted in tourism campaigns as a unique "Filipino" way of welcoming tourists (like Hawaiian "aloha"), so it acquired the meaning of "welcome" that way.
IIRC it isn't usually used in normal speech though. People will look at you funny if you go around mabuhaying everyone. Imagine, say, going around and addressing everyone with "Hail..." in English.
Anyway, context-wise it fits somewhat, because Raiden is making a (faux-)welcoming gesture here.