Complex sentence: She spends most of her time in an unused room, but turns up every now and then in odd places such as school lockers or toilet cubicles, something that Nozomu doesn't pay much attention to and just marks her attendance when he finds her.
Split into simpler sentences: She spends most of her time in an unused room, but turns up every now and then in odd places such as school lockers or toilet cubicles. Something that Nozomu doesn't pay any attention to and just marks her attendance when he finds her.