[girigiri]

Katakana is used for writing borrowed words (except for words borrowed from Chinese)

Love is written as ラブ, not as らぶ
Also パソコン (personal computer), ピンク (pink), トイレ (toilet), ガール (girl)

and for emphasis.

What DID you say?
WHAT did you say?
What did YOU say?
WHAT DID YOU SAY?
kind of deal.