To set the record straight...

In regard to one anime title...

妹さえいればいい
imouto sae ireba ii

ireba is a form of "iru" which can be read To Be, Stay, Keep, Be Doing, To Need



Instead of "A [younger] sister is all you need," the title is more like:

Good, if you need only a little sister

If all you are is a little sister, fine!

Let's break that down:
imouto - little sister
sae - ... even, only

ireba is already explained, so "ii" is Fine, Good, OK.

imout sae ireba - if you're only a little sister, or if you need only a little sister

ireba is the "if / when" verb form, so you can go further "Nice, when you need only a little sister!"