The part when Marisa saw Reimu smiling is a cliffhanger. Then takumi put flashback episodes about Marisa and Reimu's past. This is her children with Alice. Reimu want to kill them as their group's tradition has said rape children brings misfortune, but Marisa insist on raising the children.
Marisa is a beautiful yun and can quickly remarry but marrying a convenient yukkuri like Reimu may not be possible. If it was slower then Reimu would have found out.Little ones, be born quickly
Take it easy with Marisa~~