Nominative Plural: Basic Rules

The table below represents basic endings of the nominative plural:

Gender	Endings
Masculine	-ы/-и
Feminine	-ы/-и
Neuter	-а/-я

These endings are added to the stem of nouns, which is formed by dropping the nominative singular endings.

The endings -и (for masculine and feminine) and -я (for neuter nouns) are used if the last consonant of the stem is soft (so called soft stem nouns).

According to the spelling rule #1, masculine nouns ending -ж, -ч, -щ, -ц and -к, -х, -г, and feminine nouns ending -жа, -чa, -ща, -ша and -ка, -ха, -га can not add the ending -ы. That is why they will have the ending -и in nominative plural.