Additionally, I'm happier having girls here with それに〜
Grammar Explanation: In addition to with それに〜

Kei’ichi is excited about spending four days at the beach with his automobile club from university, not to mention with the Goddess Belldandy. His excitement is cut short when he hears Sayoko call out to him.
- 螢一:
- 「田宮
( 先輩( まさか美術部( と合同( でやるんじゃないでしょうね」- “Tamiya, don't tell me we're doing this with the art club!”
- 田宮
( : - 「ん……ああ。自動車部
( を題材( にしたいっていうから…… それに女( の子( がいた方( が嬉( しい…」- “It's because they said they wanted to use the automobile club as a subject... Additionally, I'm happier having girls here.”
Key Points
それに adds another reason
それに means “in addition”.
Here Tamiya gives an extra personal reason after explaining the art club’s request.
〜方が嬉しい = it would be nicer if…
女の子がいた方が嬉しい literally means “having girls there would make me happier”.
The 方が pattern sets up a comparison, even when the alternative (the result of not having girls around) is only implied.
See Also
- Grammar: Presuming with 〜だろう and 〜でしょう
- Grammar: Wanting to do with 〜たい